On paper, closer by committee sounds like a simple idea: just pitch when you're told to pitch and get outs. But it's not that simple. Like closing, getting a group of late-inning pitchers to buy into the plan isn't easy, and it takes a special group.
Pitchers (particularly relievers) are creatures of habit, and one of the most difficult parts of being a reliever is that when you get into a poorly managed bullpen you're never quite sure when you are going to pitch. The best bullpen manager I ever had was Trent Jewett, whom I played for in 2005-06 at Triple-A Indianapolis (Pirates). He was great about talking to all the pitchers during stretching to get a sense of who could give him what he needed that night. I pitched in 57 games of relief that season and warmed up only three times without going into a game.
On the flip side, after failing as a starter I was moved into the Tigers' bullpen two months into the 2000 season. The rest of that year I was called on to get "hot" more than 100 times -- I made just 56 relief appearances. It was a challenge and was particularly frustrating because it's not easy on your arm. This is the worst part of being a reliever: You get your adrenaline up to go into a game, and if it's a false alarm your adrenaline drops. Running a bullpen is the most difficult part of managing a baseball team, and some are just better than others at it.
And yet closers are mostly immune to this. The modern-day system positions them with the greatest opportunity to succeed. Teams rarely give the closer-by-committee approach a chance to succeed in part because of the problems I mentioned, but the Tigers have no other options right now and might be the one team that could pull this off at a championship level.