The film was drastically reedited before it's release because of the MPAA's ratings board strict guidelines on graphic violence, language and nudity at that point in time. Which are noticeable due to the film's many jump cuts in handful of scenes specifically most of the attacks on the strippers by the unnamed killer for example. Ultimately it caused Twentieth Century-Fox to sell of the film to an independent distributor for a theatrical release.
What are the differences between the R-Rated and Unrated Version?
For the R-Rated version the sexual tone of the movie was eased. Several shots depicting the lesbianism of the strippers as well as some stripping scenes have been removed or alternate material was used. Apart from modifications due to censorship, either of the versions contains some plot scenes missing in the other version. A detailed comparison between both versions with pictures can be found here.