CPL filter does more than that. http://nikonites.com/other-photography-equipment/2283-7-rules-cpl-filters.html
It does cut light by ~2 stops but if your purpose of getting CPL filter is to just cut out light you might be better off getting an ND / GND filter
Hello! Yes, I know. My answer was related to the previous comment. He asked me whether if I want ot use CLP for low light shooting. My answer was that I do not want to use it, since it cuts the light. I bought it for many reasons. One is shooting on the beach where water reflection can be an issue. Second is the great blue sky effect and nice contrast of landscape photos. I know it's use very well, I partly work on optics...