Whenever you plan of starting a new business, you need a good business plan. A business plan is written to structure your business concepts and ideas into paper so that it becomes easy for investors or banks to understand and finance your needs.
Business plans may target changes in perception and branding by the customer, client, taxpayer, or larger community. When the existing business is to assume a major change or when planning a new venture, a 3 to 5 year business plan is required, since investors will look for their investment return in that timeframe.
This situation is complicated by the fact that many venture capitalists will refuse to sign an NDA before looking at a business plan, lest it put them in the untenable position of looking at two independently developed look-alike business plans, both claiming originality. In such situations one may need to develop two versions of the business plan: a stripped down plan that can be used to develop a relationship and a detail plan that is only shown when investors have sufficient interest and trust to sign an NDA.
Finally, a business plan should be error - free. This is important because your business plan defines who you are as a business person. If it turned out sloppy, then that does not speak too highly of you.