I have also thought alot about that feature (and gone back and forth enabling it and disabling it on the site) This feature ties into the your website's users ability to edit their submitted link. The username and password is used for when one of your website's users submit a site and later can go back and edit their link (or site description) or other details about their submitted site. I have been running this Dew-New PHPLinks script for 3 years now and have only had 1 user who took advantage of this Edit feature but alas I still have the feature enabled.