In the past, UV filters were used to protect 'film' from UV lgith (Ultraviolet radiation). Modern digital sensors (image sensor) barely have any trouble with this UV radiation. This doesn't make the filter redundant, though. Especially at great heights, when UV radiation plays a larger role, the colors of the air will look much more natural with a filter. Because the UV protection isn't fully useful anymore because of modern digital sensors, most photographers these days use a UV filter to protect their lens. A scratched filter is a lot cheaper to replace than a lens. The quality of the filter is still important. A good UV filter doesn't show any difference in color or other negative influences on your images.