Well, this is interesting...per Jorge Arangure on Twitter, the Colorado Rockies are going to a four man rotation:
Colorado going with 4-man rotation 75 pitches per start says Tracy— Jorge Arangure (@jorgearangure) June 19, 2012
Limiting starting pitchers to 75 pitches per start seems a bit limiting to me -- I'd think it would make sense to use 90-100 pitches as a limit -- but in a year when some Rangers fans were throwing out the idea of a 6 man rotation, a team going to a 4 man rotation seems to make some sense.
The most obvious reason for going to a four man rotation is that, instead of your fifth best starter getting 32 starts, your first, second, third and fourth best starts get eight extra starts apiece. Now, your trade-off is that your starters are not going to go as deep into games as you'd prefer, but given that you have more flexibility in how you deploy your relievers than in how you deploy your fifth starter, that could well be a trade-off worth making. Also, in a National League game, it likely means having one less at bat from your pitcher, since fewer pitches means going with a pinch hitter earlier in the game than you would otherwise.
I'll be interested in seeing how this plays out for Colorado, and how long they go with it. I've thought before that there would be some merit in going with a modified four man rotation, where you keep your four "primary" starters pitching on four days rest, allowing you to skip the fifth spot when there is an off day, and then having a couple of long relief/spot starter types that you could stick into the fifth spot when need be. If you wanted to get really creative, you could rotate the fifth spot between two or three minor league pitchers, calling up a starter when you need a fifth starter and optioning someone to the minors, then immediately sending that starter back down and calling up an extra bullpen arm or bench piece who would stay up until the fifth starter's spot came around again, at which point that player would be sent down and a different fifth starter (assuming it has been less than 10 days since the initial fifth starter was optioned) called up.