Movies are an easy example: Do you want to watch the original ending of Return of the Jedi, the special edition ending, the revised ending post-prequels, the 4:

Movies are an easy example: Do you want to watch the original ending of Return of the Jedi, the special edition ending, the revised ending post-prequels, the 4:3 edition or the widescreen edition? There are plenty of reasons to want to keep a copy of the version of the experience you enjoyed and want to experience again.