Applications are often updated with newer more functional better looking templates as they are developed. For example, I'm sure many users will update applications to the latest Basic viewer included with the June 2016 release of ArcGIS Online. However when you do this you are going to have a new application URL. Users may have bookmarked or stored an older version of the viewer. If there were an option to 'redirect' users to the latest version of the application when the old retired version is opened this would be never be a problem.