Two people sitting at a desk is the most productive form of communication.  The reason is that there is a simple interaction model.  You have each person communicating and listening to only one person.  There is a reason Pair Programming isn’t called Triple or Quadruple Programming.  Each person you add to the mix makes communication more difficult.  I drew up a quick illustration of this point:

Four people isn’t even that many, but look how much more complicated the lines of communication have become. Imagine 10 people, ugh!  20 people, ack!  Think about meetings and how the communication becomes difficult with each new person you add.  When someone wants to have a group meeting for the purpose of “being on the same page”, the communication lines change from collaboration to “lecture hall”.  This is also visualized as a star-burst pattern where everyone in the room listens to one person.  The lines of communication are greatly simplified, but the collaboration is eliminated as well.

By understanding these lines of communication you can make rules about meetings.  If the goal of a meeting is to collaborate, don’t have more than 5 people in the room.  In fact, delegating to 2-3 people will yield the optimal collaborative results.  This also goes for “decisions” that need to be made.  The more people you add to the room to discuss the problem, the harder the communication pattern becomes.  Decisions will be skewed based on difficult communication.

Summary:  Fewer people = better collaboration and decision making.