Polarizing filter is generally used to remove glare off surfaces. It will cause you to loose about 1 stop of light. I use it for scenics, while never with action photography. Dependent on the angle of incident light, polarizing filter may or may not improve the subject reflectance, therefore improve the saturation and contrast. It is very useful in scenes that have water, sky, even interior architecture shots that have reflective surface.
In general, to get a proper exposure, unless you are a very experienced photographer, the Exposure Compensation button is needed whenever the metered shot appeared incorrect. The rule is: To keep white white, over-expose; while to keep black black, under-expose. It applies to everything, even in portraits. This is because the camera meter everything at 18% grey tone. To eliminate guess work, and only if you can reach the subject at hand, use an incidence meter. For a cheaper alternative, I also carry a Grey Card (18% grey) for subjects such as flower photography which has great tonal range. Hope this is helpful.
