All right, one of things Susan doesn’t ask directly (though the answer is implicit in Bob’s responses, because he’s a master at this as well as at the pure choreography of a combat scene) is this: What is the purpose of a fight scene?
I think the answer is simple. The purpose of a fight scene (or any tense action scene) is the same as the purpose of any other scene in a book. It should be there if and only if it establishes or furthers character (emotional catharsis is included here), establishes or furthers setting, and/or advances the plot. A fight/action scene doesn’t get a free pass because it’s a fight/action scene. One should never be included, for example, solely to break up a boring journey sequence (instead, rewrite the journey sequence so it’s not boring; or write the fight scene in a way that does one of the things I mention above; or write in a tension-filled scene that doesn’t involve fighting at all).
At the end of the day, readers are smart. They know a throwaway fight scene when they read it and it moves them not.
Remember that a fight/action scene is the same as any other kind of scene, except the tension in the scene requires a fight/action sequence to resolve. So apply the same standards for the inclusion of a fight/action scene as you would to any other kind of scene.