A partnership agreement is the key to keep business on track although it is not necessary.
It is a common practice that when two or more people work together, they are generally more concerned with their ideas, innovations and creative directions, rather than their legal status. However, it is important to consider and resolve the rights, roles and responsibilities of each member of the partnership in writing before a misunderstanding or dispute arises. Written agreement helps in this regards.
Remember a solid partnership should be founded on good communication.