We don't use VSS for anything. We don't invoke backups, the only backups we do are daily midnight backups of the user, domain, and system JSON (configuration) files. Those are placed into the "Archived Data" directory in every User, Domain, and at the system service settings root. They are cleaned after a couple days. You may also find a folder called "Legacy Config Files" this is a ZIP containing the user configs (XML's and such) from before the conversion. We do plan on coming out with an update that will automatically remove "Legacy Config Files" after a certain amount of time has passed.
However, this shouldn't be using a ton of space and it has nothing to do with shadow copies. This is a per user/domain/system thing. I don't have a ton of experience working with VSS so I'm not really sure what could create that.