Several years ago sociologist Brian Uzzi did a study of why certain Broadway musicals made between 1945 and 1989 were successful and others flopped. The explanation he arrived at had to do with the people behind the productions. For failed productions, one of two extremes was common. The first was a collaboration between creative artists and producers who tended to all know one another. When there were mostly strong ties, the production lacked the fresh, creative insights that come from diverse experience. The other type of failed production was one in which none of the artists had experience working together. When the group was made up of mostly weak ties, teamwork and group cohesion suffered.
In contrast, the social networks of the people behind successful productions had a healthy balance: There were some strong ties, some weak ties. There was some established trust, but also enough new blood in the system to generate new ideas. Think of your network of relationships in the same way: The best professional network is both narrow/deep (allies with whom you collaborate regularly) and wide/ shallow (weak-tie acquaintances who offer fresh information and ideas).
Reid Hoffman, The Start-Up of You