The invention process involves disclosing your invention to a wide variety of readers. As mentioned, such document is a starting point or template for providing future material with respect to the many different readers and audience for which you will need to communicate your invention.
So, although a detailed business plan may not be required for an online business, I am going to include it here so you can at least look at and consider each section and determine yourself if it applies to your business.
When submitting my concepts to invention hunts, licensing agents, manufacturers, retailers, engineers, and the patent office, I was asked many different kinds of questions. The questions ranged from "What problem does it solve?" to questions that required extensive research such as "Who is your target market?"
I also said that a business plan consists of a narrative and several financial worksheets.