Besides, your friends may be 100% behind you in your new venture, but, in case you are hoping to involve others who have actual money to invest, you may need to be able to make a convincing case. Wouldn't it be nice to have anticipated possible questions and be ready with plausible answers? If you are risking your own money, that is perhaps even a stronger reason to do some indispensable planning.
They are like fingerprints; no two are alike, even within the same organization. One further point, opinions about what makes a good finished product are like noses_everybody has one. The ones that work and prove to be executable are the best. With this in mind, let me offer my views about business plans at a macro level having written a sizeable number of plans for internal and external applications. One other point, a business plan can build a team quicker than any formal team building activity.