Although if you're doing single position training for 3 different players, if one gets subbed out, you can always dress them one of the other games to make up the difference, or go with a natural starter/backup role, and flip them for the next game. That works pretty well for getting multiple guys 48 minutes, too.
But yeah, I usually dress 6-7 players, just in the event of injury. However, I've gotten burned by that a lot recently too, so I've gone to dressing just 5.