The goal is to create one or more users whose permissions are identical to an original user on a single server.
Rather than discover what those privileges are with a SHOW GRANTS FOR statement and copy them into a script, modify it, copy and paste again for each user, etc., etc., we can use a single command to copy one user to a list of new users. We can even set different passwords for each user as we go.
Let's assume we have a user, joe@localhost, who has a long list of permissions. We need to create a clone of his user account for two new users, sally and john. Each of these users will require a new password.