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.
It becomes easy to communicate your ideas to the people you interface with, who in turn can give you better ideas or complement the ones you have. Collect all the material to one place. Having a business plan makes it possible to have all your ideas and plans in one place. It becomes easier for you refer to it and to use it to develop your business. You become a more committed business person and even others people, like your prospective financiers, can easily regard you as a serious business person.