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.
“Every book you pick up has its own lesson or lessons, and quite often the bad books have more to teach than the good ones.”
“The main object of religion is not to get a man into heaven, but to get heaven into him.”