When you’ve got a small group, you don’t need to constantly formalize things. You communicate and you know what’s going on. If you have a question about something, you ask someone. Formalized rules, deadlines, and documents start to seem silly. Everyone’s already on the same page anyway.
According to British author Antony Jay, there are centuries of evidence to support the idea that small groups are the most efficient. In “The Corporation Man,” he talks about how humans have worked in small groups, usually five to fifteen people, as hunters and farmers for hundreds of generations. The ideal group size is a ten-group:
He found the most efficient to be organised in groups of eight to fourteen people which he came to call ‘ten-groups’, each group free to find its own way towards a target set for it within the general objects of the corporation…
“The basic unit is [a group] which varies from three to twelve or fifteen in number, and perhaps optimizes somewhere around ten; that this group is bound together by a common objective, and that the bond of trust and loyalty thus formed can become an extremely powerful uniting force; that the group needs to decide on (or at least take part in deciding on) its own objective, and to work out for itself how that objective shall be achieved…”
He offers up interesting examples to back up the theory, from sports teams to juries to army squads:
Jay draws attention to units of around this size in many fields beyond the corporation. A committee works best with about ten members; if it grows much beyond that size the extra people do not take a fully active part. Nearly all team games use a group of about ten on each side. Juries have 12 members and the Jewish minyan 10. In an army, organization often decides life and death, and under this pressure armies, too, adopt a basic unit of about ten; the British army, the US army, the ancient Roman army and that of Genghiz Khan, in fact every long-standing successful army, has built up its larger formations from squads or sections of about this size.