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.
“They're talking about a movie I don't want to hold to that because in this business you can talk about things for years before they get done - god knows if the financing would happen.”
“My mother was kept very busy with her sewing; sometimes she would have another woman helping her.”