Ohhh this... when I read a post, and I feel like thinking "oh my god, that's so true, why did I just realize it", or when someone writes in simple language but has a meaning that makes me happy with the facts, it's enough to move my hand to press karma +...
Posts that even make me really want to reply, because there may be disagreements or differences of opinion, I also often give karma +, because of the interesting points being discussed.