Roof Trim Molding: Are they necessary?

I see a lot of people posting that they lose their roof trim in car washes, that they wear off, flop around, etc. I have the same issue. However, can somebody tell me whether these things NEED to be replaced? Does it actually cause damage to the car if you don't? I don't want to spend $40 replacing something that's just gonna fall off again from either weather wear or car washes.