The volunteer organization I'm with gives out candy on its outreach van. Every year, they get a big group of volunteers to go trick-or-treating for charity. I've heard similar for other places. I think it's good for those adults who didn't get enough of it when they were younger.
Myself, I'm past both trick-or-treating and parties, and am now more than happy to pass out candy and enjoy all of the kiddie costumes.