A list of categories will be displayed by default when you open App Designer or Data Stream Designer. In App Designer, this can be changed to display a custom landing page instead. When a custom landing page is set for a company, any user from that specific company will see that landing page when they first open App Designer. An App can be used as a landing page as long as it is published. This is useful if a company has a main App that they access and prevents them from continuously navigating to that App.