It used to be like once a day at least but now it's just really really dumb people every once in awhile. Which is kind of a bummer because I'm always happy to report gross pervert who harass others.
If anyone is having problems with what people are sending them, they should def report them for private message. Changing your settings might help you, but what about the next person and the messages you've already received? It's more productive to report them.