I would like to be able to manage my accounts (private information) independently of my e-mails (public information) because:
I would like to avoid any sharing of accounts between different servers,
I would like to manage differently private and public information,
I would like to be free to change one of them independently of the other.
I am highly demanding in this field to avoid privacy problems and attack exposure (through use of shared and known e-mail to start brute force attacks).
For example, if I was very security aware, and in an ideal world, my Stack Exchange accounts would be something like:
being of course managed by a secure password manager.