the simple answer is the more the better because the player's effective will last longer
if u want a simple number don't go less than 4 for everybody
if u want a player to play the full game, don't go lower than 7
the computer coach knows the effectiveness of a player on court, if he thinks a player is worse than the sup than he will put the sub in
don't count on the tatic option because it takes garbage time, and matchup disadvantage into consideration