It looks for file changes. You can customize it to skip certain files (like, I don’t have it backup my video game install folder but does everything else on that partition). Or I have it skip the .tib files (which are my Acronis Hard Drive clones) and keep them on the NAS and NOT copy them to my local 2TB drive.
You can set autosync based on time, or when the drive is detected, etc.
I use it at work to propogate a bunch of files I constantly update across multiple save locations, etc.
Very handy IMO. First time you run it, it will take FOREVER…but after that it’s really quick.