Ask HN: What is the point of Karma Points?

Everyone is always talking about Karma points or losing karma points through down voting.

As I understand it karma points to don't effect ranking of articles. Correct?

So the point of having karma points is that when you get a certain level of karma points you can down vote or flag inappropriate content.

The question is how many do you need to complete the game? How many points do you need to be able to do all of the power ups that come with getting the points?