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.
It is definitely not the most exciting part of starting a business. In fact, if you are like a lot of entrepreneurs, you are probably going to find yourself pulling a few all-nighters to get one done before heading into your first pitch for funding. Because that is the thing--your business plan is a pretty important.
Financial Plan. The financial plan section is the most important section of the business plan, especially if you need debt financing or wish to attract investors. The financial plan has to demonstrate that your business will grow and be profitable. To do this you will need to create projected income statements, cash flow statements, and balance sheets. For a new business, these are forecasts, and a good rule of thumb is to underestimate revenues and overestimate expenses.
Potential business partners need to know how their investment will be used, and ultimately, what it will achieve for the business. In this sense, your business plan is like your ambassador - showing how the various elements of your company are integrated into a vibrant whole