I have a few boxes from the 1980s that I still use for storing pieces and a few boxes from the 1990s and 2000s that I have kept just because I really love the box art. Otherwise, I recycle them (I am not a seller, so keeping for resale is not a consideration I have). Since modern Lego boxes don’t come with inserts (plastic or cardboard) for the most part, you could also collapse your boxes to save storage space.