EDIT: I think it is amazing that I have 10 upvotes, and -1 downvotes, resulting in 11 upvotes.

invite only torrent sites.

reddit used to have its own private tracker, baconBits, spawned on christmas day 2009. It shut down May of last year.

there’s plenty of others, though.

The benefit of private trackers is that since they’re invite-only, you don’t really run the risk of running into copyright cops who want to send you cease and desist notices. They generally tend to go for the easy fish at the public trackers like 1337x and torrentgalaxy. There is a sort of “circle of trust” on private trackers and it can be really easy to get your account banned if someone you invite got banned. They take the circle of trust pretty seriously on a lot of them. (That sounds more scary than it is, I’ve never seen it in practice, but the general rule is “don’t invite people who will cause trouble, because you’ll be accountable for their behavior since you invited them.”)

Also, many private trackers have an upper limit on users, and stop accepting new users when they hit that limit. Keeping user bases small also keeps you more “under the radar.”

Finally, private trackers are also a source of many scene groups releases, so if you get on certain trackers, you’ll have faster access to certain releases.