Compact team Vs Large Team

CatNigiri "compact" Team, the developers of Keen and Necrosphere

In a compact team, every member cares about the quality of the game as a whole and bugs are spotted instantly. 

In large teams developers and artists concentrate on one individual piece at a time, failing to sometimes see how their work integrates into the game as a whole.

For a couple reasons, ambitious team sizes actually slow down the development instead of speeding up the progress. Overall, look to stay lean and make sure that people who join accelerate the progress instead of slowing the team down.