If you look at the player cards for players created using the Overall method like Dan S uses for ZiPS, you'll see that there are differences in their power rating for many of them based on their handedness. Based on research I've read, it's often preferable to use historical splits to a player's actual platoon splits until you get up to an adequate sample size. I can run some ZiPS simulations now and look at how the splits turn out over 100 seasons or so and post the results some time this week if anyone is interested.