A polarizing filter has three advantages protect the lens, giving back the natural color images taken by bright sunshine (the skies will be blue as you see them out instead of white in the picture), and eliminate many reflections superfluous or annoying at the time of shooting (for example, can be photographed more easily cross a small river: the surface will reflect less sunlight). However, it is supposed to regulate the intensity of the effect by turning the filter. I have never seen any difference, as there is no manual or reference points on the ring, I might misses something.
