I leanred this the hard way, put a bra on my first car back in the early 90's, when they were "cool". After 1 year of ownership and never removing the bra. It had worn down the paint to primer in the areas around the edges and the whole nose was a slightly lighter shade when compared to the rest of the car.

 

I do take the bra off every so often to clean it. I always make sure there is wax on the car under the bra. There are minimal scratches caused by the bra however. On the other hand.... I drive 40000 miles a year. The last black car I had was sand blasted like you wouldnt believe. I thought about a clear bra but the cost was a major turn off. Also a clear bra cant do what a thick vinyl one will. I have been hit by large chunks of partical board and 70+ mph and recived nothing more than a scukff in the bra. There is no way a clear bra can protect your car from that...... And after 61+ K miles on my g with that bra, its time for new one. But I can safely say that the paint under the bra is still in near new condition, with the exception for some light hairline scratches that you have to be 3 inches from the car to see. I have some nicks for rocks that hit the hood higher up than the bra protects.... Not much I can do about that. Ill stick with my old school bra, unless I get a different color next time.