SCOTTSDALE, Ariz. -- Bruce Bochy was sitting in his office in the Giants' spring home, talking to a reporter about the value of a deep roster, when Hunter Pence barged in. Pence had yet to make his Cactus League debut because of tendinitis in his Achilles tendon, and he was not in that day's lineup. But Pence was confident he'd pass the baserunning tests about to be posed by San Francisco's training staff, and he wanted Bochy to know it.
"Tear that thing up," Pence said, pointing at the lineup on Bochy's desk. "Make a lineup with my name in it, and be ready to put it up, because I'm playing today."
Pence left. Bochy smiled.
"You wish you had 25 of him," the skipper said. "But one of the things I'm cognizant of as I go into this year is that it's important for me to rest these guys a little more. Hunter has played 162 games before. But we're going to be better if we have a player who can give us the confidence to give him a day off."

These are the kinds of conversations taking place in every dugout and every front office in Major League Baseball as the 2016 season dawns. At a time when pitcher injuries run rampant and specialization is ubiquitous, when 162-game players are virtually nonexistent and extreme turnover is inescapable (last year's postseason rosters featured an average of 23-percent turnover from Opening Day), it's no longer enough to have the most talented lineup and rotation.
You've also got to be the deepest and most flexible roster, too.
"That term 'flexibility' is a term now that's not only being used for players to have the ability to play multiple spots and do multiple things," said Cardinals general manager John Mozeliak, "but also roster flexibility where you don't wake up one day and your ability to refresh is taken away."
Because depth and flexibility can reveal themselves in various ways, let's discuss a few of them and how they apply to some outlooks for 2016.
1. Starting pitching depth
Might as well start with starting pitching, right?
By now, it's common knowledge that you generally need more than five to survive. But would you believe you might need closer to 10? Last year, 313 pitchers made at least one start in the big leagues, from Chris Archer to Tony Zych. And yes, that is a new record, folks. But beyond such trivia is the general trend, which is that we've seen an average of 9.7 starters per team per season over the past five years.
Obviously, that number includes guys making spot starts, so it's admittedly not a perfect representation of "need." But last year's raw number of guys making 30 starts (66) was the lowest since 2001, the number of guys qualifying for the ERA title (75) was the lowest in two decades, and teams needed an average of six guys to make at least 10 starts.
That's why you saw some teams target redundancy in the open market. The Astros didn't necessarily need Doug Fister, the Nationals had enough bodies to get by without Bronson Arroyo, the White Sox seemingly had a set five when they signed Mat Latos, etc. All of those clubs place a low-risk bet on a veteran in the back end as a precautionary measure.
But no team targeted pure quantity quite like the Dodgers, and we already know -- thanks to Brett Anderson's back surgery, Hyun-Jin Ryu's shoulder setback, Frankie Montas' rib removal, Mike Bolsinger's oblique injury and Brandon Beachy's arm tendinitis -- they're going to need it. But how many clubs could survive such a spring onslaught without having to resort to the trade market or their prospect stash? The Dodgers have an army of arms -- one that will grow as the above players get healthy and Brandon McCarthy returns from Tommy John surgery. The real key in all of this is that, beyond the likes of Ross Stripling and Zach Lee, the Dodgers have two prized prospects -- Julio Urias and Jose De Leon -- nearing Major League readiness. They could deliver innings or potentially be used as in-season trade bait.
"[The Dodgers] have the most depth of anyone in the league," a National League executive surmised. "The question is how they'll use it."

2. Relief depth
A deep bullpen is arguably more important than ever in the age of specialization. The average game in 2015 featured 3.11 relievers used per team (the most ever), and the average team used 27 pitchers over the course of the year. Those numbers represent a 14.8-percent and a 23.9-percent rise, respectively, from a decade earlier.
"You've got to have some optionable guys," said Marlins manager Don Mattingly, "because over the course of the season, you're going to have a couple of games where you're just blowing your 'pen up and you're going into a game and don't have any innings out there. It's not a seven-man 'pen; it should be a 12-man 'pen counting guys not in the big leagues. I had a couple teams in L.A. where you couldn't option anybody. So you're just kind of stuck."
Bullpens are inherently tough to predict or project. But just for the sake of discussion, one team to watch in this category that's not getting much love is the Twins. Nobody's going to point to their Opening Day 'pen, which includes Glen Perkins in the closing role and the likes of Kevin Jepsen and Casey Fien in setup roles, as one of the best in the game. But in Jake Reed, Mason Melotakis, Nick Burdi and J.T. Chargois, Minnesota has an array of hard-throwing relievers on the cusp who could eventually stabilize the relief situation and tear down the Twins' soft-tossing reputation in the process.

3. Position player depth
Though third on this list, this one might be creeping up toward first in importance in today's game.
To Bochy's point, you just can't count on guys to play 162. And to ask them to do so might rate as managerial malpractice in most instances. A 162-game schedule has long been considered long, but it's grown longer still given the schedule, travel and media demands of the modern game, combined with the simple reality that performance-enhancing drugs -- including amphetamines -- are being properly policed. That's why there has been so much public discussion about shortening the season or expanding roster limits.
"We're asking players to do more and more than they have done in the past," said Tony Clark, executive director of the MLB Players Association. "You can make an argument that it's affecting them and the clubs in the long run."
That's why clubs place such an emphasis on flexibility. The Orioles' Manny Machado was the only player to play in all 162 last year. Since the league expanded to 30 teams in 1998, the five lowest single-season totals of players reaching 600 plate appearances have all occurred in the past five years. Teams have determined rest to be an important factor in injury prevention, and that makes a strong bench essential.

"There are a lot of times you give guys off when they come crawling into the manager's office saying, 'I need a day,'" Cubs manager Joe Maddon said. "You want to be proactive prior to that moment. You look at what we did last year late, a lot of the teams I had with Tampa Bay have played well late, and it's no big secret. It's not special pills or better diet or travel. It's rest."
With Jason Heyward and Dexter Fowler added to the outfield stash, Maddon's Cubs rate as having one of the deepest position player groups in baseball. So, assuming good health, Maddon will be able to dole out appropriate days off. The Astros and Nationals, both of whom have deep outfield groups, are also in particularly good positions here. A little more under the radar, the A's have an interesting bench, with veterans Chris Coghlan and Coco Crisp. The D-backs have a wealth of infield options. And though the Rangers' projected lineup trends a little older, don't overlook the stash of position player prospects -- Joey Gallo, Nomar Mazara and Lewis Brinson -- they've got looming should adversity strike.

"They're going to be good," one American League scout said. "It's not just what they have; it's what they have coming."
And that leads to our last point.
4. Farm system depth
Always important, and all the more now that the game is decisively trending younger (13 out of 30 clubs were led in Wins Above Replacement by a player 26 or younger last season).
We already mentioned the Dodgers' arms, the Rangers' bats and the Twins' relievers, but you never know where the greatest in-season impact might arise. Maybe it'll be Lucas Giolito (Nats), Jose Berrios (Twins), Carson Fulmer (White Sox) or Tyler Glasnow (Pirates) boosting a rotation or Josh Bell (Pirates), Trea Turner (Nats), Aaron Judge (Yankees) or A.J. Reed (Astros) adding dimension to a lineup. For all the hype surrounding the Mets' acquisition of Yoenis Cespedes last July, the biggest factor in their trip to the World Series might have been the contributions of Noah Syndergaard, Michael Conforto and Steven Matz, all of whom were promoted during the season.

But of course, the impact of farm system depth doesn't have to be quite so direct. It can be parlayed on the trade market, too. Though it includes a couple rebuilding clubs, MLBPipeline.com's picks for the 10 best farm systems in baseball right now is a good place to start looking at teams in good position to deal.
Ultimately, though, this conversation comes with the unknown of what the standings will look like midseason and which teams will be feeling particularly frisky. Just know that the Cubs aren't likely to leave any stone unturned as they look to end the longest World Series drought on record, and the Mariners (with the longest active playoff drought) and Red Sox (with the aggressive Dave Dombrowski at the helm of a deep system) might be willing to take more chances than others.
The bottom line is that Opening Day is but a snapshot, and many of the lineups we see on that day will have about as much staying power as the one that was sitting on Bochy's desk when Pence walked in the room. A roster is nothing but a rocking boat on a raging sea, and the best teams are the ones with the depth to stay afloat.