I always tell my clients that the reason for a business plan is not to go looking for financing. You develop the business plan for you. So that you can peel back the onion and really convince yourself that you understand every aspect of what you are setting out to do.
And just as you feel that you understand all of the elements of your business something changes and you need to modify the plan. It is never right. It keeps changing and that is the beauty of planning. It is an attempt to look at the future,— at the unknown.
Here is an interesting view of business planning from someone who should know!