[przemoc]

Let me quote README file first:

    It was originally written as a supplement to git, which does not store
    all metadata, making it unsuitable for e.g. storing /etc in a
    repository.
    
    metastore can also be helpful if you want to create a tarball of a file
    tree and make sure that "everything" (e.g. xattrs, mtime, owner, group)
    is stored along with the files.

You may use it to store stuff on filesystem that doesn't support perms, owner & group for instance, like FAT, yet still be able to restore it later. Well, FAT doesn't support lot of things, so it's maybe a bad example. Anyway, I did use metastore to store metadata of some ext4 filesystem tree before backuping it on NTFS. It worked quite well.