On the rear fenders, where the top of the wheel well is, the metal bends into the wheel well at a 90 degree turn. When you go to a fatter tire in back and lower the car. The tire/wheel tends to rub the edge of the 90 degree edge, of the metal. The fender roller is used to crease the 90 degree edge into a flat edge (folding up the 90 degree). Once your fenders are "rolled" the tire/wheel does not rub the metal anymore.I've never heard of this practice. You can adjust the flare of the fender? And without cracking the paint?
I'll check out that website.