I'd say it depends on your business, and what you're intentions are for the business. Business plans are typically required for government grants, loans, and venture capital.

Although from what I've read, venture capitalists now favor the very short but impactful 10 page powerpoint slide or report that shows market need, overall product/service concept, description of current market (competitors), 3-5 year revenue model, annotate the need for cash and it's usage in how this will effect the existing revenue model vs the one with the infusion of cash, and finally distribution and market penetration goals.

Banks have pretty much frozen out small business loans, SBA small business loans plunge 57% in first quarter, so unless you already have assets that you can put against the loan, you'll have a hard time trying to get money.

There are the government grants, however, those are typically only given to non-profits and larger companies and they have very long lead times and are highly sought after in a very competitive market for grants. So if you see a program that promises easy free grants, run away.

Other than that, simply define a set of goals, a mission statement, something that you're passionate about and not just regurgitating to your employees or to a potential partner. It should be the reason you started the business and something that defines why the company is unique and and better than your competition.