Communication overhead is a quadratic function. In teams with n people it takes n^2 time to keep everyone informed.

That's why the most effective teams are wolf packs - roughly 6-10 highly performant members where communication overhead is still low enough that it barely matters, but have enough people to be way more productive than an individual.

Obviously there's a minimum level of competence you need to have for this to work. The smaller the team the less freeloaders are tolerated.

In my opinion, 4 is the best size. 7-10 is horrible - meetings and conversations use up so much time.

You want to break a team of 10 in half if you can. Not always easy. But if you can manage it, do it.