I'm not sure are you talking about cases or the cardboard box the case is held in? If it's the former I'd keep 'em if the latter I'd trash 'em.
Oh who am I kidding.... I never throw anything out!
In the early days of CDs, they manufacturers considered the difficulties stores would have displaying record albums alongside CDs....allowing them to share shelf space in a store.
To facilitate the presentation of CDs, the "long box" was created to fit the deep bins LPs were displayed in. Many (most?) CD manufacturers packaged their product in hideous, nearly impossible-to-open-without-injuring-yourself plastic long boxes. Others did cardboard longboxes, many of which featured cover art....sort of like a slenderized version of an LP cover. Many of them were gorgeous.
When it was clear LPs were a thing of the past, store owners upgraded their shelving. The longboxes -- much-hated by most consumers (even the artistic cardboard ones) were phased out. They were never designed to store the CD, and you had the dilemma of either throwing them away, which pained me, or saving them, which is also a pain.
Dan (the Man) obviously retained some beautiful cardboard long boxes with poster-quality art on them for the cast albums. You can't find these today...ANYWHERE. So...it's probably best not to trash something like that because SOMEONE, SOMEWHERE will want it, admire it, value it...and LUST after it.
It's even better to make something practical out of it...like a piece of art...and make your friends PEA-GREEN with envy!