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.
“It's a funny thing - when I'm crazed with work, spending time with my children relaxes me. Yet, at the end of a long weekend with them, the very thing I need to relax is a little work and time away from them!”