The response below yours is correct but for me the big thing is with the coach mode settings on you no longer are the intelligence for the Qbs, Rbs etc.
With Qbs/rbs that makes the the game because I like most others want to see a real difference between one Qb/RB to the next. Also with Rbs in theory you should see a difference in the good from the bad based on their vision and the holes they hit. Those two are most impacted because they are the ones we control the majority of the time when coach mode is off.
I do take control of the players when necessary and on defense I control one player throughout each play.