Although under-used by average LinkedIn members, LinkedIn Groups can be critical to a successful job search because they enable you to communicate directly with recruiters. And vice versa. You can leverage Groups for both visibility and credibility, demonstrating your knowledge and communications skills — when you use Groups with care.
LinkedIn members can join up to fifty Groups, although LinkedIn members belong to an average of only seven. My strong recommendation is that anyone in a job search join all fifty, at least while in job search mode.