I saw this discussion in the comment section of some post, and it was about what the vote should be used for and how there is no official guideline for how to use it. I thought this was such a good question, that it deserved a post of its own. Related question would be if there should be multiple scores with different meanings, through which posts can be sorted.
Some possible meanings: high/low effort, good/bad argument, agree/disagree, funny/lame. I more or less expect all of those depending on context and the type of post/comment itself. Often combined.
What some people do is to vote based on the relationship with the author. Some people always downvote any comment by a person they hate. The opposite also exists.
Hm.. Yes. I am guilty of this. I would not say I always upvote/downvote, but the bias exists.