How People Limit their Social Networks

In the early days of social media I remember this discussion about how broad one should cast their social network.   A number like 40 people in their network was suggested.  Lately, though, there did not seem any natural limit in place.  This article from Oxford University appears to say it occurs naturally. " ... Despite the way that mobile technologies and social networking sites have made it easier to stay in touch with large numbers of acquaintances, a new study has shown that people still put most of their efforts into communicating with small numbers of close friends or relatives. We often operate unconscious one-in, one-out policies so that communication patterns remain the same even when friendships change.  ... "