In real estate parlance, it is said that the three most important factors in maximizing the value of your property are location, location and location.  Networking carries a similar importance, especially for those preparing for a career beyond NIH, or your current institution.  Many good jobs are filled by candidates who have been identified prior to that job being officially posted.  Therefore, the more broadly your net of contacts can be cast, the better your chances of receiving advanced information on positions which are of interest to you.