Some people with very expensive lenses would not put a filter on the end, as optically it would not be as good, but would protect the lens knocks and finger prints, with a lens hood.
A UV filter can act as a lens cap, protecting the lens, but you are always ready to shoot.
UV filters can vary in price. I have bought cheap filters from ebay. Very cheap filters can be basically glass with no UV coating and may reduce the quality of the image. You will notice this when shooting towards the light. You get what you pay for.