I have full flaps plus PPF and the front flaps help a lot with the door issue. After a highway jaunt (especially through the winter), I still see marks on the PPF, just not nearly as many. I am assuming the flaps stop the pebbles from going directly to the back doors, but they still may drop to the ground and bounce back up to the same spot at a lower relative speed. I will keep both in place. The rear flaps actually keep the back of the car a lot cleaner if nothing else. It used to be covered in dust within a couple of miles after a wash but now it takes a few miles : )