It makes the passing look better... also you'll see a few more organic misfires and no roboQB.
It's 4 accuracy ratings: SAC, MAC, DAC, TOR (throw on run).
I know it seems like a pain, but it's really only 2-3 minutes of time before and after each game, and well worth it.
I was running -20, but that was a bit too much at times.
-10 was not quite enough.