For example, there was a scene, an important scene, in which there was a death in a place containing thirty people.
It was a deliberately confused scene and my detectives interviewed several witnesses to try to ascertain what had happened.
Interviewed too many people, in fact. Three characters pointlessly repeated each other and one was created entirely for the scene and did not appear anywhere else in the novel.
So, the first two characters had their lines cut and it also became clear that the newly-created one really was not needed at all so I deleted her.
The result? A scene with added pace and zip and much cleaner narrative flow.