Not sure yet. Probably many small files. Mostly docs & pics, but also Thunderbird profile/emails, Firefox profile, some (portable) tools etc password/profile files.
I'll check it out. I've been using FreeFileSync (portable version) to backup/sync manually my USB-stick (contains many tools etc).
Gonna try installed version FFS. It says in features that it has:
Automate sync as a batch job