At every start SS IPTV requests playlist from the URL
and if it is successfully loaded places its tile on the Main Screen
The app requests this playlist in any case, no matter if user's ISP is registered in system or not. It means, you can provide easy access to playlist for your customers, just configuring DNS, even if your company wasn't added to the list of supported operators.
At the same time, registration gives operators much more flexible opportunities for content distributing, including getting from users authentication params (login/pass, device identificator etc)
In order to provide sure playlist loading on any device, the server must return it with http-header Access-Control-Allow-Origin. All the requirements and opportunities about playlist's structure are also valid for playlists in local domain