I would not phrase the means of approaching best length as "edit out everything that's not 100% necessary" but as something more like "make every scene count/pull more than its weight". The former, to my mind, tends to associate with small goals and a pure utilitarianism that falls short of excellence. I doubt you meant anything like that.

I certainly agree that "Great scenes will server two or more purposes". A scene can advance the plot, display who the characters are and who they may become, foreshadow or rationalize future plot elements (or present red herrings), introduce worldbuilding depth, manage the emotional state of the audience (comic relief is a simple example), etc. I would not be surprised if a great scene can also so elevate other scenes that its relative greatness may be less obvious because it makes the whole greater than the sum of its parts in isolation.

I very rarely watch movies (even less often in a theater) and I do not have a drama or fiction writing background, but even a "little learning" about the theory hints that bulk is easier to achieve than extensive excellence.