What are you up against?
You are well on your way to taming the dragon so you may walk it or fly it at your leisure. A sound business plan is your map, it's the compass you use to walk the dragon in the right direction.
If you can't explain what your business does in one line, chances are the business is either not focused or clear enough about where it is going. While there are numerous success stories of business-plan-on-a-napkin, it pays to think through what will it take to . . .