I absolutely hate this and rarely see anybody who uses this. I remember back in NCAA 09 where they had a similar Player Lock system but not to an extreme of where you cannot "unlock" and switch to a different player in a middle of a play.
In NCAA 09, I would run a pro-style offense, running the ball and using play action to help create passing lanes. When running the ball, I would Lock (it made my icon turn red) on to a Offensive Lineman and I would usually get a nasty pancake block on a DE or DT, then it would automatically give me the control of the HB as he is handed off the ball. This created big holes for me to run through as I can manually hit certain running lanes I saw, without relying on the CPU to run right into a defender.
Yes, my running game was pretty good and I got good chunks of yards but what made my offense lethal was my play action game. Now imagine if I was getting good rushing yards out of a certain formation, came out with the same formation, locked on to my lineman to make it look like it was a run, but it was actually play action. I mean it was money. Even though I was locked onto my lineman presnap, as soon as he faked the run to the Running Back, I would get control of the Quarterback and hit an open target. It worked great against all different types of players, especially people who manually controlled their Safeties.
When they took this out of last years game, I've seen less people take snaps under center and more out of shotgun. I was really hoping it would come back for this years so I can go back to a conventional offense. Maybe I'm the only one who was doing it tho?