Depth has never been more important in the game, and being able to fill in for an injured player or pick up the slack for a struggling one are key components for any successful team.
Some players are more easily replaceable -- even for short periods of time -- than others. This week, we take a look at who the most indispensable player is on each team in the National League West. In some cases, it's the team's best player, but not always.

D-backs: Paul Goldschmidt
The D-backs didn't need a reminder of how important Goldschmidt was to the lineup, but they got one in May. The six-time All-Star had a miserable month, and he was hitting just .198 on May 22. It was no coincidence that the D-backs lost 15 of 17 at one point during May and finished the month with an 8-19 record. Goldschmidt provides not just outstanding offense, but he also is a three-time Gold Glove Award winner. There is no obvious alternative at first base, with the D-backs sometimes using Daniel Descalso there when Goldschmidt gets a rare day off.

Dodgers: Kenley Jansen
He's not only the most indispensable player on this team, but maybe any team. In the Dodgers' first five losses after he went on the disabled list with an irregular heartbeat, each game was lost in the opponent's final at-bat. Even though he hasn't been as dominating as previous years, Jansen has still been so good he made his third All-Star team. And the Dodgers realized his value, making an exception to their usual stance on not handing out huge free-agent contracts when they inked Jansen to an $80 million, five-year deal.

Giants: Buster Posey
The six-time All-Star catcher influences the club's fortunes almost daily. Though his hip problems have muted his offensive numbers and may require season-ending surgery, Posey remains the one Giants player who opponents tend to skirt in tight situations. He manipulates the bat extremely well, making him the ideal man to have at the plate under any circumstance. Defensively, Posey remains an expert receiver who's skilled in the art of pitch framing. More importantly, he commands the trust of San Francisco's pitchers, who have been bright spot for the team. Additionally, Posey's ability to play first base gives manager Bruce Bochy some flexibility in assembling each day's lineup.

Padres: William Myers
The Padres' lineup is just different when it's anchored by Myers -- as they learned the hard way this year. Myers has spent three separate stints on the disabled list. When he's healthy, Myers is a force, and his upside on offense rates higher than anyone else on San Diego's roster -- even Eric Hosmer. Myers' newfound versatility has become important for the Padres, too. He can play across the outfield, and he's added third base to his repertoire. That's allowed the Padres to give opportunities to a handful of youngsters, based on matchups.

Rockies: Trevor Story
The Rockies have strong starting pitching and stars all over the diamond, such as third baseman Nolan Arenado, right fielder Carlos Gonzalez, center fielder Charlie Blackmon and second baseman DJ LeMahieu. But it's tough to come up with a workable Plan B if something were to happen to Story, with former top pick Brendan Rodgers currently on the Triple-A Albuquerque disabled list with a left hamstring injury -- plus being 22 and still learning. Story's power can help transform the lineup, and his glovework helps support a pitching staff that is driving the Rockies' push for the postseason.