I've managed to delete a folder with GBs of important data because Syncthing has non-obvious ways of handling data. Thankfully, I have tons of backups of everything, so it wasn't a big deal, but since then I've been extremely paranoid when using Syncthing to make sure it doesn't happen again.
I do all my work with Syncthing in send-only folders, one per machine. Which means that if I make changes across machines then I always get duplicates, but the redundancy feels natural - it's only concerning if the data size becomes absolutely huge.
