Ask HN: Why does HN show the score of posts?

I've noticed that when I look at a post I'm occasionally more inclined to upvote when the score of the post is high (or perhaps higher than when I last visited HN).

This is a disposition of my own, of course, but now I wonder why the score is there at all. Or at least why it's shown on the main page.

Is it possible other readers also have this disposition to upvote a post that is trending or has a (relatively) high score?

What would happen if the score wasn't shown at all?

(I should probably note that I don't have down-vote privileges, but I'm not sure what factor that has in this context.)