This is one of those community manager situations that can be unpleasant to deal with. If this is just one user, your best option is to contact that user and make it clear that you value the input, but that it's too much and maybe stifling the other users. It's tough to find a nice way to say that someone should tone it down, but it's sometimes necessary.
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 .