Administrating the MySQL Server - Mastering phpMyAdmin 3.4 for Effective MySQL Management - page 329

After clicking on Go , bill no longer exists in the mysql database. Also, all of his
privileges, including the privileges on the bill database, will have been transferred to
the new user— billy . However, the user definition of bill will still exist in memory,
and hence it's still effective. If we had chosen the delete the old one from the user
tables and reload the privileges afterwards option instead, the user definition of bill
would immediately have ceased to be valid.
Alternatively, we could have created another user based on bill , by making use
of the keep the old one choice. We can transfer the password to the new user by
choosing Do not change the password option, or change it by entering a new
password twice. The revoke all active privileges… option immediately terminates
the effective current privileges for this user, even if he or she is currently logged in.