Besides this in the vast majority and I mean 99.999999% the cropping has no benefit to the dog and mearly serves as an ego boost to the owner.
There are a lot of reasons that some breeds are traditionally cropped and/or docked. While I much prefer a natural dog, I'd rather see it just go out of style, rather than be banned outright, because people who really want their dogs cropped and.or docked are going to do it regardless. Having it done by a vet who uses proper anesthesia and surgical techniques, and providing proper aftercare, is much preferable to most of the options I can think of.
And yes, sometimes ears and/or tails are amputated (fully or partially) at a later date, due to injury or tumors. I had a car who had an ear cropped when she was spayed at 6-ish months, because she had some kind of growth on it (she had it when I got her at 6 weeks), and it was bothering her.