Remember Required Fields
If this option is checked, it will remember the “required fields for login” that are defined in the module.
What does this really mean? If someone logs into your site, then logs out, then goes back to the login page, their email address, user name or other defined login field will be remembered so that they will not have to type it again. This is really a user experience feature and is using the cookies in the browser to remember this data.
More information for this and other DNN Login Module features.