Mormon Life says: Some good information here.

The current movie rating system in the US gets a lot of criticism – most of it deserved. However, it also gets prematurely dismissed as unhelpful and irrelevant.
It’s not irrelevant. A movie’s rating – subjective as it is – still presents information about that movie.
As an example, suppose you see the following films on a movie store shelf and have absolutely no information about content other than the title:
If you had the ratings to go by, you’d know that in this list one movie is G, one is PG, two are PG-13, two are R, and one is NC-17 — isn’t that fairly significant information when making an informed decision? There is a big difference between a PG movie and a NC-17 movie, obviously, and movie rating in a general (but accurate) fashion reflects that difference — helpful for knowing if a “Kids…” movie is, you know, appropriate for kids. Most movie rating debates happen at the margins — the border between PG-13 and R, for example — but in the broad, general categories they are meant to represent, they provide useful information when making decisions. (No one gets into debates about the rating given to a book, for example, because books don’t have ratings at all!)