When I am logged out and I browse a random post I see this:
Note the little question below. What is that for?
It is for anonymous users to vote on the quality of a post.
It gathers opinions from people with no account or little rep in a way that doesn't affect the user or the poster's reputation.
That is an option for unregistered users to express their feedback regarding the quality of a post.
It also does not affect the votes of the post.