I certainly disagree with the Crowdstack analysis referred to above. I make extensive use of topic notifications and eliminating this function would cause a significant decline in the functionality of the forum.
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 .