I disagree. Give me a chance to explain.
As a photographer and business owner, and sometimes analog and digital assistant, there has been little proof of social networking sites providing much (if any) business benefit. It is also important to realize that any work posted on ones site (especially sites such as "Facebook") requires legal permission from clients. Most often, the only [legal] work allowed is that done personally by the photographer (which may not reflect the crux of their business, i.e. headshot photographers).
Beyond this, a personal/business site outside of Facebook provides a much better conduit for branching out online. Making certain you're advertised well and in the top brackets of search engines helps a great deal (in essence, the "old school" of internet marketing). Statistically (fairly consistent research), empirical studies [comparing businesses in the same market/locale over a one year span] between non-Facebook advertised businesses (traditional), business who ventured into Facebook (both traditional and non-traditional), and business purely on Facebook (non-traditional), little difference (if any) was demonstrated.
Facebook consists vastly of private individuals communicating with friends and family. With millions of individuals using the social service each day, advertising is consistently pushed aside/ignored by many (Safari extensions, etc allow for the removal of [some] Facebook ads, in the same vein as YouTube cleaners).
Does any of this really help photographers/businesses? Not really. It simply helps Apple and Zuckerberg.