There are two main purposes the lens hood has to serve. Number one is protection, at least in my book. A lens hood will save you from a lot of unexpected and certainly unwanted events and incidents that involve some kind of impact between your lens and something hard. Let's say you're shooting your son's soccer game with a 70-200 mm f/2.8 and a kick sends the ball in your direction at a really high speed. Not having a lens hood on would definitely cause massive damage. Forget about the UV filter. Even a premium one won't help you in case of direct impact with a fast ball and even if the ball doesn't touch the front element of the lens, the fragments will most likely damage it. So the first purpose of the lens hood is protection.