Just using the Joomla core to limit complete access is to adjust permissions on menus, article and modules and in some cases use a second template or figure out a way to re-purpose the offline mode function which isn't optimal in most cases. Either way it's a hassle when all you want to do is hide everything, including the template to your site.

With this plugin, you can hide everything except a login block to force your registered users to login to gain access and spend less than 10 minutes setting it up.

Perfect for an intranet site or website that you don't want visible to the world.