This subject has been beaten to death in previous threads. Keep in mind you will find people on both sides of nearly any question here. Use the search function and do your research, then decide for yourself.
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 .