
The lens on your camera is its eye to the world, and should the front element pick up any scratches or scrapes, that's not good news for the images you'll subsequently take. So it makes sense to keep it protected.
Many photographers use UV, skylight or clear filters primarily as protection for the front element of their lenses. But with the light from your subject having to first pass through the filter on the lens, quality matters. A second-grade filter will result in second-grade images.