I'm not really a fan because in a lot of cases it forces you to download stuff you might not want just to establish and maintain an acceptable ratio so eventually you can get the stuff you do want.

if I wanted something obscure and not really interested in the popular thing I'm either wasting bandwidth and/or server space starting out or searching for that thing on a public tracker.

the one private tracker I do use is extremely generous with upload credits for newbies and I was able to take advantage of that plus contribute something right away so I didn't and still don't have any issues but I know that's not the case with some people.