I've written a few business plans in my life (3 started companies, 2 sold, current one is Series A funded FWIW). Every single time, the plans sat on the shelf.

I've written a few business plans in my life (3 started companies, 2 sold, current one is Series A funded FWIW). Every single time, the plans sat on the shelf. Every single time, I looked back at those plans and laughed/cringed at the assumptions I made in them and was amazed at how little my business resembled the picture I painted in those plans. I think it's a great exercise to run through the sections that are common in biz plans (marketing, etc). Think about 'em, talk about 'em, maybe even through together a spreadsheet or two. But don't make it formal and don't spend too much time on it-- the more you invest in it, the more it'll feel like a blueprint rather than an exercise.