This is a pretty common call amongst the junior marketing staff of my clients, most of them are familiar with facebook, they use it in their personal lives to fill a whole range of functions.
When asked “Why must we be on Facebook”? there is usually an awkward silence, and the standard response is likely to be something like “just because!”
Facebook, Twitter, and all the others are just tools, they are able to deliver an outcome, but it is the outcome that matters, not the tool, used to get there.
You measure the performance of a car on a journey in many ways, petrol mileage, comfort, handling, and so on, but the reason you get in the car is to get somewhere. Social media is no different, measures of the media themselves are just measures of efficiency, not measures of the outcome.
To make it worthwhile, to create engagement, to build a relationship, there must be something for the traveler at the end of the journey.