That SAS ad is just a pop up---nothing to do with the SOC site. As soon as it became apparent that SAS was who they are Theron booted them along with other change that vastly raised the quality of this site's discourse.
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 .