Background and Foreground Action | Filming
Each person in background or foreground movement should have a purpose. Simply to walk down the street is not sufficient. To stop at a store window, contemplate a memory and then to enter the store is everyday behavior with a purpose. People in the background may no be consciously seen by the audience, but they will be missed if omitted.
Every person, whether in the background or foreground has a purpose and adds to the mood of the scene. Everything must be thought out carefully by the director in order to deliver the message they intend to deliver. Every little piece is essential in telling the story.