I haven't tried this at WDW but at some other hotels, I'll put my empty suitcase under the bed to save room. Some people like to put their dirty clothes in their empty suitcase until they leave, which saves having the dirty clothes out in a hamper.
We do that on cruises; with limited closet space, it is easier to just place the dirty clothes in the suitcases in the closet, rather than using the pop-up hampers.