To configure Site Closure you first have to make a Site Policy in the top level site settings under Site Collection Administration.
In the Site Policies page you can click create to make a Site Policy. When you create a Site Policy you have these options available to you.
If you select the second radio button "Delete sites automatically" you get more options.
If you choose the last radio button, "Close and delete sites automatically", you get one more schedule option available to you.
Once one or more Site Policies have been created you apply the policies to the existing sites using the Site Closure and Deletion link on the Site Settings page under Site Administration.
So as you can see, it is a simple feature but enables the SharePoint administrators far greater control over removal of sites in a typical user site creation scenario.
In addition to the above Site Policy settings, you can enable Self-Service Site Creation forcing users to select a Site Policy to apply to their site. Finally we have the ability to clean the unused sites out of SharePoint without a delete only option as in the past.