Well, perhaps not all. Let's give a little credit to the playwright's taste and sensibility. Everything needs to be edited carefully, of course, but not everything the author likes needs to be thrown into the flames just because it has met with the writer's emotional approval! Only the things that don't fit or don't ring true. Only the things that slow the action down instead of moving it along.
Case in point: I have written a scene that I hope some day I can use, or use at least part of it. It's a scene in which Shakespeare and members of his theater company are reminiscing about their experiences together over the years. It captures a certain quality of Elizabethan London life, its earthiness and rowdiness. Its rough humor. I had written it for my first play, then called "Shakespeare in the Dark," when I was still reaching for the right ending. It didn't work there! Oh, Lord, it didn't work anywhere in that play. Nor was there any good place for it in the next. A friend of mine read the scene and really really liked it. He said, "Surely you can make your play a few minutes longer and include it." And I had to say, "But there's no place for it in the story arc of the play. It's an extraneous blob."
I haven't thrown it out, expunged it from my computer; so I won't say that I've killed it. But I have put it in a little place to rest. May it have warm covers and happy dreams. And perhaps someday I'll wake it up and say, "Up now! Get up now! You're on!"