Oh my, on some Forums this simple question will start a waterfall of opinions pro and con. I have flaps behind each set of duels, but I also have a wide flap on the rear of the coach. Now some will say that it causes rocks and such to fly up striking the toad and have taken them off. I have not. The key is to have the flap high enough that it will not drag the pavement. That's what causes the rock to fly up. Mine clears the road by about six inches when fully aired up. I have had no chipped paint.
Is it for the toad or the coach? Well, in my opinion it's for both.