This is a good question actually, when you have managed proper form and know your body and limits, weak point and so on, it is by all means ok to add lbs and go sloppy. Just play it safe.
I sometimes bounce the bar in benchpress, i do power shrugs with half rom sometimes, and my bb rows tend to get more upright when going heavy. Its the heavy weight that chocks your cns and forces your body to grow, not doing light reps standing perfectly still and focusing on "mind-muscle" and other BS.
Proper form is something you should master, but not depend on.