Creates a login name that is separate from the forum username. Can be controlled via the ACP / UCP.
The MOD will allow users to keep the same login name while their username (screen name) can be changed to whatever they like. This saves users forgetting their login name if "allow username changes" permissions are enabled and the users constantly change and their username.
The MOD can also add another layer of security if someone tries to access a user account thinking that the username is the loginname, the attacker will be trying to access a name that doesn't authenticate, this is only however if the user creates a different username from their login name.