How Important Is a Business Plan?

Have you written a business plan? That's the question Scott Shane, a professor of entrepreneurial studies at Case Western Reserve University, poses to entrepreneurs in his latest New York Times small business column. According to Shane, academic research of the business start-up process shows that many entrepreneurs never write a business plan, regardless of the positive impact it can have on developing a product, organizing a company, generating sales, ect. There are several reasons for this, he suggests:

1.) Entrepreneurs don't know that they are supposed to write one or realize how it could help them.
2.) Writing a business plan doesn't have the action-oriented appeal of hiring employees, setting up shop, ect.
3.) Entrepreneurs are afraid that testing out their idea too much will show them it's not viable.

What do you think? Is a business plan necessary? Share your thoughts at the end of the column.