Scene of Performance in Movies

Scene of Performance in Movies

These three specific movies contain what we might call “ scenes of performance”, in which characters act or put on a show for one another, and we become aware of our own status as spectators.
What is the purpose of such scenes? How they are important to the surrounding narrative in which they appear?
Scene to consider: The fork-in-roll dance that the tramp performs for Georgia and her friends in” The Gold Rush”
Vienna playing the piano in “Johny Guitar”
The orchestral scenes in “Russian Ark”
*no need to put introduction you can jump into argument