It's very nice to see that X people liked a post/comment and Y people disliked it instead of just having a singular "goodness/badness" rating. It (literally, in a mathematical sense) adds a whole new dimension to post ratings and gives us a more nuanced understanding of people's opinions. Plus, it feels a lot better to see that 5 people agreed with you and 7 disagreed when you made a controversial statement instead of just seeing a score of -1 telling you how bad you are.