It occurred to me today how useful I find the history palette in Photoshop. The history palette for anyone new to Photoshop, remembers everything you do. If you add a filter, a brush stroke or select something it will remember it. The good thing is if you then decide you want to remove a particular filter because you preferred the document without it, you can. Simply open the history palette and you can click to go back to any previous state and so discarding the recent changes.