This setting is intended for testing - enable and compare this menu to your main menu.  It will add UberMenu to your site via the wp_footer() hook and fix it to the top of your site.  This allows you to test the menu without interference from the theme's menu (in the majority of cases).  It is a good way to test if you need to use Manual Integration.  You will need to assign a menu to the UberMenu [Direct Injection] theme location