A business plan lays out the market you are after, your objectives, the strategies and tactics you will implement, the key performance indicators, the resources you’ll need to achieve your plan, and finally the financial plan and milestones.
Last but not least, a business plan gives you a reference document. How are you doing against what you set out to accomplish? Are you ahead or behind? What’s different from the assumptions you started with? If you are on plan, great! If not, what do you need to do to get back on plan?