TL;DR: Great to have if you're looking for less popular content, high quality files, and/or are concerned about copyright notices, but the rules that keep the niche content alive make them less appealing for super popular content.
I randomly made friends IRL about a year ago and got an invite to BTN & PTP. I don't watch/download a lot of movies, so my account at PTP has lapsed, but I've kept my account with BTN.
From my recent searches, BTN tends to have higher quality files and more seeders than public trackers, but since a) I have a seed box, which provides a line of defense against copyright notices, and is only strengthened my my *aars (gets me in & out of the swarm before the studios find it), b) I usually can't tell the difference in quality from the devices I'm using (and my friends/family most definitely don't notice/care), c) seed ratio or time doesn't impact access to public trackers, and d) I prefer to keep public torrents alive, I usually lean towards public trackers, and only use the private trackers for things that are harder to find and/or things I want in high quality.
I still try to seed to a minimum ratio of 3.0 on popular files (public or private), and ∞ for more niche files, but sometimes demand is so low, and I need to move files off of my seed box. While a ratio below 1.0 makes me feel "stuck" no matter where I got the file from, private tracker rules definitely amplify that feeling.