The Archive is a place where you can throw any of your stuff that’s not currently relevant to you, but may be in the future. The Archive can hold Lists, and all of the stuff inside of them.
You can use the Archive however you’d like. Essentially, it’s just a place to throw stuff that doesn’t need to be top-of-mind at the moment. You can always dive back in and un-archive a Space or Lists when you’re ready for it again later.