I have never used one. I suppose if you photograph in sand storms or driving rain, then protection would be nice, but I see no need to filter out UV. Sometimes color photography at high elevations renders blue sky an unusual color, which it is, and maybe then...
To me, adding a UV filter is just something in the way to degrade the image. If I were going to use one on anything but a wide angle lens, I'd buy the cheapest one I could find. The glass that your lenses are made of stops all wavelengthes shorter than 350nm.