It’s now possible to set up a closed social network, a la Facebook, for a limited group of users such as a company. Sort of like how some companies have a private internet (called an intranet), they can have a private Facebook (called an enterprise social network). You get the benefits of collaboration, networking, custom business apps, etc. It’s sort of like what Lotus Notes did back in the day.
Enterprise social netowrking is not hypothetical—the linked article discusses how the Royal Bank of Scotland is deploying Facebook at Work for 100,000 employees. And most notably, it’s an opportunity for Facebook to make money selling a product, versus selling advertisements.