Using % for host when creating a MySQL user

My MySQL database needs two users: appuser and support.
One of the application developers insists that I create four accounts for these users:

appuser@'%'
appuser@'localhost'

support@'%'
support@'localhost'

For the life of me I can't figure out why he thinks we need this. Wouldn't using the wildcard as the host take care of the 'localhost'?

Any ideas?

(Using MySQL 5.5 here)

Answer

localhost is special in MySQL, it means a connection over a UNIX socket (or named pipes on Windows, I believe) as opposed to a TCP/IP socket. Using % as the host does not include localhost, hence the need to explicitly specify it.