Captured thinking: You don't allow your financial people to keep their numbers in their heads. Financial reports are the lifeblood of the numbers side of any business, no matter what size. It should be no different with marketing. Your written document lays out your game plan. If people leave, if new people arrive, if memories falter, if events bring pressure to alter the givens, the information in the written marketing plan stays intact to remind you of what you'd agreed on.
In addition, unified understanding of marketing plan according to experts that according to MC Donald. According to Strategic Marketing Planning is a management process that leads to marketing planning. Planning is a logical sequence and a series of activities towards the determination of marketing objectives and formulation of plans to achieve goals.