Film ratings, in use in Canada since the 1950s, and in the United States since the 1960s, are often considered more progressive than censorship. Ratings presume that children need more protection from film content than adults do, and that everyone benefits from warnings about content. This may be true, although films that are suitable for all ages can act as a unifying social force, and can make a lot of money. Films targeted to age groups are an aspect of cultural fragmentation accelerated by the internet, and are not necessarily a good thing.
Ratings influence content in two directions. A film maker or distributor seeking the widest possible audience may self-censor, before or after production, in order to achieve a lower rating. A famous case of this was the post-production changes to Stanley Kubrick's Eyes Wide Shut (1999). Kubrick was contractually required to produce an 'R' rated film, and when the final version was determined to be NC-17, objects were digitally added to block the offending content. When obtaining a rating requires removing or blocking content, ratings are no different than traditional censorship.
On the other hand, a film targeted at a specific audience, for example teens, may deliberately add content to ensure a film rating high enough to make attendance cool. While adding material might seem the opposite of censorship, it is still a case of regulations influencing content. Rating films is more progressive than cutting or banning films, but it is still censorship.