You don't have to flesh out your bit players as much. How much depends on their importance to the story. A waiter is just someone passing through and needs very little description or fleshing out. The guy opposing the protagonist at a zoning committee meeting needs more fleshing out. His motive for doing so should be clear. People have motivations for what they do. When people are mean, there's a reason, and the same when they're nice. The more these reasons are fleshed out, the more real the story feels. While we don't need a waiter's motivation for serving our food explained to us. More complicated actions require more fleshing out to understand.