There isn't a legitimate reason to link to /newest unless it's to promote your submission, which in itself is against the HN rules. (there is the belief that people who vote in a submission via /newest do not trip voting ring detectors like that of direct links, but that is false)

Is a voting ring defined by people being friends, in a similar geolocation, voting at a similar time, voting together consistently historically, or what? In other words, what distinguishes a voting ring from simply a group of users with similar interests or a small niche community?

Linking to /newest appears to many HN users to just be a way around directly linking to their article.

I don't know enough about the voting manipulation detection implementation on HN, but I'd imagine a bunch of accounts hitting a direct link to an article and upvoting it could potentially be more suspicious than having them all click the article from /newest or just upvote from there.

FWIW as an anecdote, I've seen HN voting manipulation kick in quite hard when people link directly to submissions.

I think I recall reading somewhere that the upvotes a story gets on the /newest page weigh more heavily in promoting the story to the top main pages, than the upvotes a story will invariably get when its on one of the first few main pages.

I don't have a reference for that, however, and I don't know if it is true or not.