It's a half-tier between discussion and main attempting to alleviate scaling issues.

A better solution would just be to implement a full tier between discussion and main, or to create a new tier above main. Sample proposal (I'm not going to do this, so I don't expect anybody else to do this, this is just an example structure):

Discussion remains as-is. Main is consolidated into a single tier. Promoted is created as a tier above Main, with some multiple of the karma values, but requires a buy-in of, say, 500, or maybe 1000 Karma Points for each post placed there, and automatically demote any post in Promoted which gets below -10 Karma and stays there for a full day. Default users who aren't logged in to Promoted as the new "main" page. Additionally, create a new members-only "Social" board where meet-ups and off-topic conversation can be engaged in; Posts and comments there can be upvoted and downvoted, but have no Karma value.