For a normal street car, it's just gives it look to make it look more aggressive. For rallying, in those cars such as the WRC cars, they perform a function but I don't know what. I think they look pretty cool, but if it doesn't do anything, then what is the point of getting it? But it's for looks, but I wouldn't want it because I would be afraid people would say, wtf is that and what does it do, you said say nothing and they would be like, "oh you put that and it doesn't do anything? thats gay"
but I mean it don't matter. I still like them.