From this Business Week article… (Source)
Employees that were rated as more innovative didn’t have bigger networks; rather, they had more bridging ties—ties that connected them to other employees who were themselves not connected.
If we are circulating too much with people we have known forever or people who themselves are all spending time in the same meetings and interactions, then we are not getting the performance impact we can from social-media tools. Bigger is not better. The magic lies in the new ideas and perspectives that can come from connections into different networks.