Here's a question from a PhD looking for a position in the Medical Device industry.  He had spent the last several years with university start ups and was seeking to make the jump to an established Medtech company. 

His inquiry was whether inviting industry recruiters to join his LinkedIn network would help his job search.  I can count on hearing a form of that question at least weekly.  What he was really asking was "Does a recruiter find jobs for people?"  Of course my answer is an emphatic "No!"  It's actually the reverse. 

Unless you're timing is perfect (you should buy a lottery ticket as well), the best you can hope for is to end up in a candidate database.  But guess what?  At least in the case of LinkedIn, a recruiter can indirectly help someone find a job!  As a member of my LI network, the candidate gains more search capabilities in the medical device vertical (i.e. my network).

Their potential to reach hiring managers and networking resources is enhanced. Since I'll also be gaining access to his or her network, I'd call that a win-win!