Pitchers don't platoon, position players do. Say you have 2 third basemen with comparable fielding ability. One hits the heck out of right handed pitching, the other hits better against lefties. A manager will "platoon" these players so one starts against righties and the other against lefties. They don't play every game, but share the position depending on the situation.
Hmmm, I think maybe I'm getting confused with a scouting line from OOTP 6.5, as I own and play that game too. [:)] The reason I switched to Puresim is that I found OOTP to be a little too complex for me, and Puresim looks that little bit easier, especially without the waivers and other complicated stuff included in the game.