Teams are important for helping to galvanize individuals behind a common purpose and making the best use of complementary skills. Teams also provide a system of internal feedback.
Individuals working alone may waste excessive time on a flawed idea or strategy. As part of a team, there are more individuals to point out flaws and suggest alternatives.
Working in teams helps to boost morale, not only through the sense of a shared vision or goal, but by increasing the pace of a project. There is also a therapeutic quality built into teams, whereby a team shares successes and perceived failures together and learn from the experiences.