This advice came in very handy today, as I was editing Book 2. I realized I hadn't properly described some elaborate gardens of a Manor which plays a key role in certain scenes.
Well, long ago, in Book 1, I recall that I had spent time describing said gardens in great detail. But -- while editing that first book, I'd removed that scene entirely. So, today, I went in search of that scene. I found an old version of the book, saved from 2007, and after some scrolling down and looking around, Voila! There it was, the two paragraphs of description I needed.
I love it when that happens. And even though it took me a little bit of time to find the scene (probably just as much as it would have taken to write it again, fresh), it was worth it. Because that particular description happened to be just the one I needed.