Comments like yes, no, agree, disagree, good post, and lame are concise, but also boring wastes of time which add little to a discussion. The aggregate measure of those sentiments (as expressed in a point total) is both more concise and of some value, as it serves to encourage and highlight good posts and discourage thoughtless or pointless comments. It also provides a relatively unobtrusive outlet for those who wish to voice appreciation of thoughtfulness; this is preferable to the sea of "agree"s and "disagree"s that might spring up in the absence of a point system.

I feel such comments when presented like news.yc votes or FriendFeed likes add more value because of their conciseness.

  (define (value conversation-element)
    (- (benefit conversation-element)
       (cost conversation-element)))

  (define (cost conversation-element)
    (- (conciseness conversation-element)))

I'll leave the definition of (benefit conversation-element) as an exercise for the reader.