I used to be in a private tracker for spanish media some years ago.

Pros:

Curated content: good quality, everything was what it said it was and had the quality they said they had. And is often good quality.
Availability: authorities were not locking the web all the time like it happens with public trackers.
More content: in this case it was Spanish content, which can be hard to find sometimes in public trackers, specially good quality content.
Amazing speed and seed ratios, even for older torrents, everything was seeded and the speed was supperb.
Better search: everything had to be posted following a format, so searching was really easy.
Less malware risk: everything is well moderated so very small chances of running into malware.

Cons:

Strict rules: like very strick rules, you can get kick out really easy.
You have to seed: that's the point, and it's good etiquette while torrenting, but sometimes it is a burder having to fill the seed ratios for your torrents.
Sometimes they ask you to have specific hardware and connections to be able to join. Like a server with a seedbox.

I was incredibly happy with the tracker, but it suddenly closed one day, we found latter than the admin died, and nobody replaced him. To this day I haven't been able to enter another spanish tracker as all I know of are closed for new members. And english private trackers I've tried but I was kicked for inactivity, as it is true that for english content public tracked are not bad at all, so I wasn't using it that much, and inactivity is often cause of expulsion.