As a business major and complete dork, I disagree. However I do know that the idea of writing a 15 paged plan isn't appealing to most people. Unless you are applying for a loan, you don't NEED a business plan, but you should make a mini one.
Handy one page digital marketing plan to help you grow your grow your digital visibility and business. This one page plan lends itself to adaptation and changes in keeping with the agile marketing methodologies of today.