A plan may be essential in order to prove that your concept is viable when it comes to talking to investors or seeking funding from other sources. However, even if you are independently funded and have nothing to prove to anyone a plan will still be useful. It will help you to confirm that your plans are indeed possible and it will give you a place to compile all the data that you collect from your research.
Many small businesses take a "fly by the seat of your pants" approach to operating their businesses. For example, let's say that an excellent business opportunity arose for you, an opportunity that would net your business $5,000 over the next 3 months. However, in order to take advantage of this opportunity, you need an initial cash outlay of $1,000. Do you have the resources necessary to take advantage of this opportunity?
The most important aspect of business planning (the "What does it all come down to?" part), however, is spending the time to do your research ("due diligence") and critically thinking about these various aspects of your business. Of course, it is impossible to anticipate every detail simply by spending time thinking and writing; it is for this reason that plans are referred to and viewed as "dynamic". However, the more issues and scenarios you are able to come up with ahead of time, the more prepared you will be to handle these as they arise.
Outline any competitive advantages that you may have. Do you have any catering business qualifications or skills? Have you have experience in the hospitality industry? Do you have existing relationships with suppliers or prospective clients?