By making a business plan, you can pick out any potential flaws that might hinder you. It's a good chance to find any problems or issues that may arise, and then deal with them accordingly before you get caught up in the business. Also, outside parties can cast a fresh eye over the plan, and may pick out something that you may not have spotted.
A good business plan communicates one's ideas to people, communicates his mission, objectives, management approach, responsibilities and demonstrates how one's strategy will increase profitability and performance, identifying his audience without overreacting his aims and objectives of his business plan. A business communicates in two ways- Internal communication and External communication. Internal communication includes communication of corporate vision, shared value, strategies, guiding principles and employee motivation. External communication includes branding, customer relation, marketing, advertising, media and public relations etc..