I dont see any reason at all to have more than 12 players.
If you are worried about getting too many minutes grap a really cheap player off transfer list while the injured player is out. Just use the scrub on your scrimmage games or a game you can easily win.
Seems like teams with 10-14 players have good game-shape and function well.
Less than 10 or more than 14 it just seems people cant get enough minutes to keep people in shape to play.