Schools need a principal so they have someone that is in charge and acts as a figure head during meetings and so there is someone that the teachers can go to when needed. The principal will solve disputes between students and teachers, students and students, and even teachers and parents. They are very needed.
Until our education system receives a complete overhaul, school is for behavior modification. Our school system was created to teach immigrants to behave like "Americans" instead of their own cultural behaviors. Until the system is changed a principal helps to maintain order in schools. The principal fulfills an important role in this manner.