When a NXT customer looks for applications they see a short description of the application and a link for more information (most likely the app developers website) on the Available Apps tab.  This description and the URL are carried over to description of the application on the Connected Apps tab.  The NXT user sees the Connected App tab and description after connecting the application.  If you created a separate field and URL for the Connected app, this would allow developer to show a different message and URL when the app is connected.  The message and URL could contain "Getting Started" instructions, account sign up, or whatever else the developer thinks is useful for the NXT user.  By default it could contain the Available App language if the developer does not want to create a second message.