I'd like to add another reason to others already posted: if your player is much better at shooting or driving than the player guarding him is in OD or ID, he will get fouled more and have more chance at being injured.
I witnessed this in current season where I'm training my SG on C. This of course is an extreme because I have been playing him in cup against Centers with 1-4 in OD and he has JS 14, DR 14. But he got injured twice in a row; once just for the game and next time for 1 week. I have a Level 4 doctor.
So if next time you want to field your JS 12, DR 12 SG against a bot in cup and play Patient, think twice