There are many reasons for utilizing such a document. Is the final document going to be about implementing a decision already having been reached or is it about analysis and recommendations for a newly proposed activity. As noted above, a finished document may be for internal or external purposes. Externally they are often used to solicit funding for a start_up or joint venture. Whatever the purpose, do not confuse effort with say, a marketing or a production plan.
So, why is business planning so crucial? In a word, it provides "clarity". Investing time to develop a plan provides precise clarification of the company vision to both employees and customers. In addition, it provides a mechanism to gauge the results of the business and provides the foundation for future growth plans. In the long haul, it enhances the company valuation through fiscal responsibility, which provides the story of opportunity to any future investor or employee. In short, the benefits of planning allow the company to articulate a common vision to align resources and make an efficient use of investment dollars. A company that is perceived to be a "well_oiled machine" is attractive on many fronts _ both externally with investors and internally with employees through job satisfaction and increased tenure.