If a document needs to be developed that requires input from other disciplines_Finance, HR, Property & Facilities, Marketing, Procurement/Supply Chain_ then most likely you are looking at a team building effort to get the job done. In any event, don't look at the task as only as a roadmap that leads to a profitable product or enterprise. Business plans are a great way to build team buy_in, force a thorough review of options, define objectives, establish benchmarks to judge performance, and help arrive at a plan_of_action. Ultimately, it can lead to a Project Management approach to implementing a plan and that can be as involved and detailed as is necessary.
As I conclude, I would like to advice all people, who want to start any kind of business or who already have business without a business plan, to think about creating one as way to building a successful business. One of the causes of failure in business is lack of proper planning. Create a business plan if you want to succeed in your online home business!