Not sure if you mean keeping track of total upvotes or just the voting system in general. In either case, just for a start, I think discussions are easier to have & follow along with when someone can just upvote a comment to engage in the discussion vs posting something like "+1" or "^ this" or "I agree", and the number is the same feedback in lieu of meaningless posts. Voting also helps with ordering (as opposed to time based ordering), whether your total karma is displayed or not.