Thanks to Ash Maurya's Lean Canvas, you can focus on what exactly your business will do and not get scattered with other ideas. This also give you a 360 degree view of your business and allow you to communicate your idea better.
Business Plan Mind Map - that's exactly the level you should look at this topic in an early stage startup environment. Use it as a brain teaser, be very selective (e.g. don't worry about balance sheets etc.) and don't overstrategize. Stay humble and lean and capture your initial data in the lean or business model canvas - not in a heavy business plan document.