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.
So why make a business plan? I want to show you a totally different kind of business plan. What if you made a business plan that focused only on what you want for your life? You have dreams about what you would like your lifestyle to be, right? Why not make a business plan that could give you those dreams? What would your business look like if it gave you exactly what you want in life. What kind of salary would your business need to give you? Why not build a business plan around that? Decide how much salary you would need to support your dreams and then build a business plan that would show exactly how your business could give you that. Wouldn't it be better to have your business work for you instead of the other way around?