First, my strong bias (which I find is reinforced in many places, including this book) is that all "real work" these days takes place in teams. (Yes, Virginia, I need to add some caveats, but it's still basically true. IMHO.)
Chapter Five of their book is titled: Applying the Team Discipline: Number & Skill. Subhead: "A small number -- ideally less than 10..."
They then give 6 long reasons why large groups are not teams (or, at least, don't have the discipline of a winning team, as they [and I] see it). I will summarize:
- Large groups cannot easily or frequently meet together.
- Large groups are biased toward efficient meetings. [Why is this a bad thing?!?! Well, efficiency is not creative, for one.]
- Large groups are biased toward hierarchical leadership.
- Large groups are biased toward stable roles.
- Large groups usually fail to build common understanding and commitment.
- Large groups often subdivide ...[and] create smaller teams [sub-teams].