I’ve been thinking about these buttons, what they do, and what do I want to convey when using them. Just using them to convey what I agree or disagree with comes quite naturally, but I don’t think that’s the best way to do it.
IMO a better way would be to upvote when I believe that more people should see this post or comment, and downvote, when the society as a whole would benefit if fewer people saw this stuff. I may personally disagree with something, but still believe that this stuff is good for other people to see. It’s all highly subjective, so clearly right or wrong answers in this regard are bit rare.