Any funder worth his or her salt wants to see it right off the bat. Moreover though, a solid business plan is a living document that will continue to guide your efforts as your business grows. A lot of those mistakes (most of them, in fact) are the result of poor planning. Bad location, a marginal niche, having no specific user in mind, raising too much or too little money--all of these issues can be prevented or at least mitigated with good planning.
A business plan gives an outline of your business, the market in which it will operate and how it aims to make money - and should answer this question: why will your business succeed when so many others fail?
Be specific. Being specific is just as important as being concise. The details will help you drill down into how you will actually deliver your plan.
Sample business plans and templates can help you develop a professional document that will serve as an in-depth marketing tool to convince others of your venture s potential for success. However, creating your own plan can be a complex process, and you may need the assistance of a professional (like an accountant) depending on the type of business you have (or want to run), and what you are seeking in terms of investment.