Here is a recap of where we are in this discussion: Business plans formalize an understanding of the task with appropriate analysis leading to a plan_of_action. Not all business plans are for profit motives. Business plans are for an enterprise effort and not focused on disciplines/departments, e.g. Marketing plan, sales plan, HR plan, supply chain plan, etc. Business plans are a great vehicle to build a team effort. Plans can be utilized for formalizing metrics relative to achieving goals and performance measurements. Some complex plans might include a Project Management professional. There are internal and external audiences for business plans. Most external focused plans are for outside funding of projects. Be mindful of the 'tone' the plan projects to the reader. Tone refers to the impression a person gets from reading the plan; a subliminal feeling about the plan.
If you need to get going quickly to ride the wave of a fad before it fizzles, then fast, bare_bones planning may be all you've got time to execute. This works best when you've already got the infrastructure in place, perhaps from previous projects or an established business, and you can simply shift energy and resources to the new idea.