When your team is smaller it allows for better engagement and fewer feelings of inadequacy. As the number of people is small, the effort from each member is increased causing there to be a rise in productivity and output. Feeling inadequate stems from ideas that aren't shared for fear of ridicule or looking less intelliget. In a smaller team these feelings are reduced as the pool of people who can share ideas and insights is limited and it's usually all hands on deck.
The other reason why smaller teams are more efficient is because their communication is much more effective. It's easier to keep in touch with a smaller group than a big one (we all know what that WhatsApp group is like). People's words or suggestions usually go unnoticed in larger groups. In smaller groups, everyone is aware of the other and know what everyone's responsibilities are and how to help them if needed.
It goes without saying that smaller group meetings are more productive, efficient and have tons of innovative ideas. With smaller groups, ideas are kept to a decent amount, the next idea will most likely be a 180 of the previous one, paving the way for more innovations and a feasible plan to move forward with.
The smaller the group the less drama there is, the less drama, the more work gets to be done. No mystery there really.
Better engagement and less feelings of inadequacy
Communication is more effective
Original and innovative ideas