The best backup is a proper 3-2-1, with regular testing of integrity, and regular restoration from a backup as an exercise. But most people cannot be bothered to care quite so much.

So, keeping a half-assed backup copy on a spouse's machine in a different room is still better than not keeping any copy at all. It will not protect from every disaster, but it will protect against some.

My own backups progressed from manual rsync to syncthing to syncthing for every machine in the house + restic backups (which saved my bacon more than once).