I used to sync 300 GB with #Syncthing. Now I'm syncing 5 MB with N#extcloud. It's baby steps. I'm still doing double backups of the entire filesystem (#DejaDup and #rsync) to separate USB hard drives....
In addition to backups, I had two desktops pretty much mirrored with that huge Syncthing sync. While it was convenient in a lot of ways (and not so much when there were conflicting changes), I'd rather have one primary data hub and lots of backups and then pass the things I'm working on through the sync and not everything.