Devising a business plan forces you to think about how your company will make money. It makes you examine whether your product or service appeals to the masses or just one small group — such as graphic designers who work on Macintosh computers.
If your product or service is meant to save its users money, you'll need to examine the importance of that claim. A product or service that saves your local mechanic $20,000 a year is probably worth pursuing; one that saves a big company like GM or Ford $20,000 annually may not be worth the trouble.