During the regular season, Jorge Posada is more important to the New York Yankees than is Carlos Gomez to the Milwaukee Brewers. Wade Davis is more important to the Tampa Bay Rays than is Koji Uehara to the Texas Rangers. Come playoff time, though, those things cease to be true.
October is a fickle time of year, and opportunities to claim small but critical advantages abound. Every win and every loss is nine times as valuable. A run in postseason play is the equivalent of a full win in the regular season. If a team can milk even a small advantage from clever deployment of personnel resources, they derive huge benefit.
Unfortunately, those advantages cannot be achieved in the easiest and most efficient ways available in the regular season. There are no fifth starters. Because of travel days, backup catchers rarely play at all. Those are key areas of depth on many teams.
Another is platoon talent. During the regular season, two decent players can be worth as much as one very good one, given that each can lend their team the platoon advantage much more often than average. Not so in the playoffs: Those gains come by volume, and even if Desmond Jennings will face CC Sabathia or Jon Lester a bit more often than is ideal, you would rather have him than the combination of Ryan Raburn and Andy Dirks in the postseason.
Once a team reaches the tournament, then, they are better served by having a deep lineup, but a shallow and specialized bench; a rotation fronted by two great starters, rather than loaded with five steady ones; and a bullpen stacked with two or three key stoppers, not a deep squad of good specialists.
If all that is true, it should be clear: There is depth that matters in the playoffs, and there is depth that does not matter. Here follow rankings of the 10 teams still in playoff contention, based not on their total team depth, but on the guys who will matter to each if and when they get to the dance.