It's only important for the investors to whom it's important. In my experience the more hoops you're asked to jump through by an investor, the less likely that investor is to invest. Creating a business plan is a good exercise though, and worth carving out time for as an exercise in planning and projection. But for very early stage startups, so much is going to change that a demand for a sophisticated, detailed plan doesn't really make that much sense. I'm all for results first.