Scenario (which has happened to me a couple of times):
Suppose I record a change which I call A. Then a second change B which depends on A. Then some time later I discover that everything I had done in change A was a mistake, but I still want to keep everything in change B. It would be inconvenient to just unrecord A because I would have to redo B (and possibly several other changes). A better solution might be to record a new change which is the opposite of A and then resolve any conflicts which arise.