Do you really need a business plan?
First, I want to share my bias because this question, like lots of other entrepreneurial ones, has no perfect answer. I started my entrepreneurial career while very young when, I think, there were typewriters but well before there were personal computers and software products such as Microsoft Word or WordPerfect (I am definitely dating myself with the WordPerfect reference). So, had it occurred to me at the age of eight or nine to write a business plan for my lawn cutting business, it would probably have been more work than benefit.