Does having a blog, tweeting, activity on LinkedIn or some other social presence benefit a candidate?

While you are in job search mode, be deliberate about every move you make on all social media outlets. First, ask yourself if you are supporting or saying anything controversial. That includes anything political, religious, sexual, drug-or-alcohol related, racially-sensitive, or can be construed as discriminatory. Be sure to clean up prior posts about the above, as well. 

Social media activity that can help: Using LinkedIn to join groups in your field of interest (the industry and job type you are targeting). You can forward insights from industry and field leaders and adding a comment. However, just staying "clean and quiet" is okay, too! Simply don't give a recruiter, networker, or hiring manager a reason to put you in the "no pile," metaphorically or literally.