I'm not too interested in the "tag" vs "path" debate. For my use case (IMAP server) I don't think it makes any real difference. Many people use virtual users, where all users' mails are stored using
the same UNIX UID. For extra security it is possible to chroot into a user's mail directory though. So I'd primarily want to avoid any potential ways to get around that chroot into other users' mails, by preventing syscalls that just aren't necessary.