So since no one has explained it....taping it up keeps the wheels from getting dirty and keeps bugs from getting smashed on the bumper??? Just a guess.....
its both, keeps rock chips and bugs off, youd be surprised how much damage is done by bugs on paint their guts eat through the clear coat and make it impossible to be smooth again, even after claybar, especially if you dont wash it right after the trip, with tape all you do is peel it off, much better than scrubbing bugs off.