You don't really turn it off. You click on the capture setting and turn capture on and off. The camera is still running , etc. but it is not sending data to the software.
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 .