cactus
That is only true if you want to access the system from remote hosts and localhost under the same username, otherwise one of them would be enough.
As I understand it, for localhost access you only need to use
user@localhost
but if you want remote host access, then you need to use both
user@localhost and user@%
(or a specific host address ie user@IP)
I did say usually, and the subject was remote host access.