Their activities may fall outside the scope and focus of the company, and they won't be providing needed information, thus making the organization less balanced and less diverse. This diagram shows an evenly balanced company with a strong hierarchy governing the flow of information. The trick in any company, large or small, is to eliminate as much as possible of the bureaucracy, and minimize the hierarchy. I'm suggesting that not everything should have to go through formalized channels. People who demand this are usually just insecure and trying to micromanage.
Channels do give management control, but they also reduce the flow of information.
So you need to allow some back channels for both informal and direct communication. They also have some idea of what is going on elsewhere, which tends to make them feel more secure about their activities. People in the dark are usually afraid, and formal communications are almost never enough to keep every group brightly lit. If you have a team or manager building completely autonomous groups, ones that aren't interacting or communicating with the others, then they aren't serving a clear purpose and are not likely to live up to their potential. If each area is isolated and can communicate only through formal channels, then it would probably be a better strategy to outsource that function, since the advantage of having it in-house is the communication and feedback that others can gain.