In general, yeah. Private torrent trackers tend to focus on specific types of content. Some might focus on cartoons. Some might focus on anime. Some focus on books. Some focus on video games. Public trackers, on the other hand, generally focus on everything, which, of course, means they won't have a lot of the older or more niche stuff, and they might be lacking in one or more categories (music, anime, books, TV, etc.).

It's also much less likely that a torrent on a private tracker will die because most private trackers enforce certain rules about seeding and because the people there are generally much more into seeding than most people on a public tracker. (Probably most people on public trackers simply download what they need and stop before seeding anything back.)

Private trackers are also typically the first (and sometimes only) places to get scene releases. Scene releases, which are done by private groups, are usually higher quality than stuff on public trackers. Sometimes, they leak onto a public tracker, but not usually.