"System Volume Information" is not specific to System Restore at all. (The restore points are actually kept as Volume Shadow Copies starting with Windows Vista. Shadow Copies are used for other things such as the "File History" feature, which also store their metadata in that folder.) The folder also keeps various other kinds of NTFS metadata, and the file you mention is used is for tracking NTFS object IDs.
(So… if you claim you know "the" purpose of this folder, then you don't know it.)