The reality is no matter how much you work with things in your head, no matter how confident you may be and how much you think you already have a great vision for your business, there are so many great reasons why you should get it down on paper.
Describe the manufacturing or operating process and associated costs. Contain believable finical projections, with key data explained and documented.
Be Prepared For Risks : It is a fact of life that any new business or enterprise has a degree of risk attached to it. Therefore it is important for your business plan to analyse and calculate that risk, showing how you will engage with it. There is no business plan out there that is risk-free, but very often where the risk is higher then the rewards will be as well.
Most of all if you are seeking funding for your business, it will be absolutely crucial to go along and show someone an actual plan, because there will be very few people who will loan you money on the basis of what's just in your head. So it's pivotal to have a plan and be committed to preparing that document.