I'm thinking of a use case where a user registers for the site and rather than being told they'll be sent an email with registration details, the user is set to inactive and told an administrator will review the access request prior to granting site access.
This way, the site administrator could use the profile data gathered during registration to (for example) make decisions on which group(s) to add the user to etc prior to activating the user and emailing a confirmation.
I'm thinking I could set up something like this by adding custom code to the LoggingIn event (http://software.sharepointsolutions.com/support/knowledge/excm/Pages/excm0018.aspx). Before I go that route I thought I'd check to be sure the functionality doesn't already exist in the product or that I've missed an easier solution.