There's a lot of content on private trackers that's not available on the public internet, especially when it's more local or obscure content. You'll always find the latest US tv shows or Hollywood movies everywhere, and will for many years but when you want to look for things like Austrian movies from the 80s, a specific country edition of a given CD or a vinyl ripped with a specific turntable and needle you'll need to be on a private tracker or private forum.

If that's not what you are after, it's not worth it. It's just a very specific hobby.