I save everything. I am angry because a friend of mine worked on my computer and eliminated some "useless" stuff - bits of paragraphs saved as single words. I would be able to find them. Not anymore. They might have had just the right word I needed.
I have made many errors in "saving." I've written over important documents and even novel iterations that I wished I had today. Sometimes the original is really better than the final, polished, perfectly written and grammatically correct in third person work with no soul.