It potentially spares website creators from worrying about user management, encryption, data persistence, data portability, and some aspects of scaling. Also, it allows users to give sites permission to access their data, and to revoke that permission.
Perhaps it's not accurate to call this "promising", as I don't think anyone has promised that this will be possible, but I think the web would be more open if a substrate like this were used more.
Does it need to be saved? From what?
A promising technology would do it?