Important: This action will permanently delete all content and user information, but the hard disk space will not be immediately ...

Important:  This action will permanently delete all content and user information, but the hard disk space will not be immediately available. When you delete a large site, SharePoint removes data gradually for performance reasons. To perform an immediate deletion, you need to run a set of commands using, for example, Power Shell or the Object Model. Find more information, see the SharePoint Help system.