A lot of the writers in my critique group find it easier to write new material than to self-edit: slashing out pet phrases, paragraphs or whole pages. Not me. I think I prefer self-editing and the whole rewriting process. It's as if my first attempt is a blurry picture and I need multiple edits to bring the characters and story into focus.
I can edit my work and re-write anytime, even if I have 15 minutes available. By contrast, to write a new scene, I need the right conditions: at least an hour, minimal distractions, a clear head and no fatigue. Focused time like that is a rare commodity for me.
I have a whole file of 'early versions' of my novel saved on my computer, versions that involved a different protagonist, scenes that I decided not to use, or plot lines that were dead ends.
I don't know why I'm saving them. Maybe they'll come in handy sometime in some other novel. Or maybe they are all just part of my learning curve.