That's fine if all you want is to backup or sync bookmarks. A cloud solution is much easier. But I also want my passwords, emails, settings, all backed up encrypted and easily restored from one folder. Would be too tedious to setup sync relations with each file. Much easier to just sync one profile file.
I stopped using SyncToy since WIN XP as you can only sync manually. I'd rather use an app that just needs to be setup once, and than does it job automatically without the need of periodic intervention on my part.
In reality, I have two backups on separate drives on top of the source drive.