A reason not to throw your trays

I had kept all my trays up till now (on tray 21 of 26) and did not think there would be a reason to keep them. However think about this scenario. Lets say you finish your treatment and now have reached the point that you have to use your all day retainers or even the night only retainers and default them ( forget to wear them for an extended period of time), if your teeth move, you could go back to one of the recent trays and bring it back right? Any orthodonists here?