To make local backups I have to do them on schedule, transfer all photos (or rsync them) from all devices to backup media. To have some redundancy I have to make a copy (unless you got a RAID NAS at home that is). In this situation you’ll have a backup as recent as your sync frequency. To access the backups you have to browse the files on the drive, if it’s a NAS, it can be quite convenient, but not if it’s any other kind of storage.
Compare this to for example Google Photos backup. You take a photo, you have Internet connection, it’s synchronized. You don’t worry about redundancy, and can access the photo wherever you are with a very nice app.