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.
“For him to have understood me would have meant reorganizing his thinking... giving up his intellectual ballast, and few people are willing to risk such a radical move.”
“The real cure for what ails our health care system today is less government and more freedom.”