It automatically syncs changes ~1 minute after edits, these syncs take very little bandwidth (unless you regularly attach massive files to your notes, which you shouldn’t be doing). If you haven’t made any changes nothing will sync.
On another note, you should not be using sync as a backup method, it’s meant for syncing and has the potential for data loss if things get screwy see this chain. You should export your notes regularly if you want a proper backup.