The way I had it explained to me was, it is a measurement of your participation in the community. If you have four posts, you have four karma points. In the bottom left corner of each posting it shows the number of posts you have participated in, or created. If you go into your personal zone your karma points shuold be the same. I think that is the deal!
When you block a person, they can no longer invite you to a private message or post to your profile wall. Replies and comments they make will be collapsed/hidden by default. Finally, you'll never receive email notifications about content they create or likes they designate for your content.
Note: if you proceed, you will no longer be following .