I think you’ll probably also find that the “spare” bedroom in many houses ends up getting used for other things—storage, a hobby room, (famously) perhaps an office or second office.

My spare bedroom has a futon couch but I actually use the space for various other things most of the time. Most people may have space that’s underutilized much of the time but that doesn’t mean it’s sealed off until they have an overnight guest or a large dinner part. Things aren’t that binary.