Look at the Coen brothers. All their minor characters are as interesting as their protagonists. If the smaller characters are well-written, the whole world of the film becomes enriched. It's not the size of the thing, but the detail.
“I have tried to be as eclectic as I possibly can with my professional life, and so far it's been pretty fun.”
“Oh, you hate your job? Why didn't you say so? There's a support group for that. It's called everybody, and they meet at the bar.”