It's naive to think this recycle bin is purely there as a way for Facebook to keep your data. Facebook can already do that (just because it appears deleted to you doesn't mean it's actually deleted) and there are both nefarious (this is Facebook after all) and legitimate reasons to do so (keeping deleted posts in a moderation queue so that rule-breakers can't just quickly post & delete forbidden content before moderators have a chance to review it).
You can access 'Recycle Bin' with the icon on the top of the page, next to the archive option, just in case you've thrown away something you want to keep.