Growing up in rural Iowa, I learned that rodeo clowns are useful in distracting agitated animals. In venues like Cirque du Soleil, they entertain (or distract, if you're not amused) between acts.I'm not afraid of clowns, but I've never enjoyed them, either.
I don't really see their point.
And the friendly ones, like Bozo, actually do entertain children.
Basically, they're distractions, and they liberate you from your children for a couple hours. That's about all.