Business plans are mostly about organizing, formalizing, and committing to a specific plan_of_actions. Such a document generally presents the objectives, strategies, analysis, and a detailed roadmap for implementation. Underlying a plan_of_action is comprehensive analysis of historic, current and proposed results all supported with assumptions. If anyone doubts the interest in business plans, a Google search returns more than 62 million and Amazon list more than 77꺜 titles concerning this subject.
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.