Hi Paul,
It does exactly what it says. It won't allow Super Administrators to log in to the front-end of the site. This feature is there in order to prevent an attacker from brute-forcing your Super Admin password, i.e. try different random passwords until he finds the one you're actually using. Remember that your site has both a front- and a back-end and you log in to both with the same username/password. That's why it may be a good idea to block SA logins in the front-end.
Nicholas K. Dionysopoulos
Lead Developer and Director
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