You are saving them for a special project...that you haven't thought of yet.Honestly, they increase the footprint of the cage, they don't catch much debris (I have to sweep anyway) but they do catch a lot of poop, and they are harder to clean than the mats on the floor are.
I haven't used these in over a decade. I have a pile of them in my garage. Frankly, I don't even know why I save them.