Quote Originally Posted by LateNight72
Flanging the quarter has the ability to de-arc the quarter panel. Basically when you flange it, it will try to force the quarter panel flat.



Imagine taking a piece of sheet metal that has a curvature to it. Then imagine what the metal would do if you put a 90º bend in the panel perpendicular to the curve. Essentially that is what you're doing when you flange a quarter panel.
The effect will be pretty minimal... you are only flanging about 1/2" each time.