I totally *disagree* about bras.. Bras don't cause paint problems, but they may expose them..
I've had a bra (hood portion only of a cheap "Le Bra", I never use the bumper cover) on my old Corolla for pretty much 15 *YEARS* straight (with very infrequent removal for hand wash/wax- basically maybe once a year, if that; most of the time I just drove through the car wash, with the bra on).. There's no noticable color shade difference between the covered and uncovered portion, but where the exposed paint is covered with swirls and light scratches, the covered portion is still glossy and new looking, clearcoat is perfect and intact.
On the flip side, my previous car was a second hand salvaged Tercel with a cheap white Ziebart paint job.. In this case, the covered portion displayed a noticable yellowing vs. the exposed portion, but likewise, it was also shiny and glossy compared to the exposed portion..
I got my Prius second hand, and the previous owner did *not* get any kind of hood protection, and so the hood was incredibly pitted with stone and dust impacts, most right down to bare metal and showing light rusting and virtually impossible to retouch (to repair the paint, you'd have to completely repaint the hood).. I cleaned off the rusted impacts with one of those fibreglass cleaning brushes and touched up as best I can, but I've currently got a genuine Toyota bra on it. Even if it causes paint fade, which I'm not convinced of, I prefer the protection vs. having my hood beat to hell by stones and road debris (most of this occurs in the winter time when they put down a mixture of gravel and salt on the roads), besides, even if the paint fades, it's covered up and you can't see it (the bra looks a lot better than the original sand-blasted pitted appearance anyways), so what's the big deal?