[Untamed]

That depends on how loose it is. When the wind buffets the bra, it can cavitate something fierce, which is what pulls pins loose that hold the front bumper cover. As long as its relatively tight against the bumper, you should be ok.

I'll leave the aesthetic part of car bras out.

You will also want to pull it off from time to time to ensure nothing gets trapped between the bra and the paint. Stuff trapped inside can rub and scratch / remove paint. It doesn't happen often so this is not a weekly, or even monthly thing. Car bras can protect your car from the bugs and small objects that fly off other cars and trucks, so its worth it if you really do a lot of long distance driving. Highway driving to and from work may not require it.