2 main advantages:
-
no hosting liability. Unlike torrents; you're not seeding ie hosting the files yourself. You're purely downloading. This moves you out of the crosshairs of copyright holders as they are only interested in the hosts (providers). This also means a VPN is not necessary for usenet downloading. (providers don't log who downloads what either)
-
speed. As long as the content is available (hasn't been removed due to dmca/ntd), you are always downloading at the maximum connection speed between you and your provider. No waiting/hoping for seeds and whatever their connections can provide. I'm usually at around 70mb/s. Where as torrents very very rarely broke 10mb/s for me, usually struggling to reach 1mb/s.
As far as availability goes, stats from my usenet client: of 17m articles requested this month, 78% were available. I'm only using a single usenet provider. That availability percentage can be improved by using more than one in different jurisdictions (content is difficult to remove from multiple servers across different regions).
That's not been my experience at all. Pretty much everything I've looked for has been available and I rarely come across encrypted files. I do regularly have to try 2 or 3 nzbs before I find a complete one, but I almost always find one.