There are several reasons to think over updating your business plan:
A well-made business plan is not a one-time product. You may use this valuable business tool when examine your actual position and planning a successful course for the future. It is the chance to make sure you've chose the right way. Some business people leave behind their plan after they raise funds. But if you keep the plan up-to-date going forward, you can turn it into a useful business tool.
Intending to found the company, you wrote the business plan and tried to persuade investors of your success. You predicted a lot of things such as future markets, your production demands and capabilities, and your customers' needs. As a result you got the projections that were just a guess about how the future would play out, and requested for money based on that imagined future.
Updating your plan gives you an opportunity to look at the whole picture and make sure it still makes sense. You see what is underway, what your assumptions failed and which ones came true. Realize whether you've been right about your markets, which predicted benefits your product has and which ones has not. Precision of competitors' anticipation is also important. The second review of your business plan let you indicate all the issues again and decide whether or not you're on track.
The business plan is your action, and treating it as such will help outline your future course. Financial Plan also requires revisiting as it contains such important information as headcount numbers, expenses, sales growth and so on. Determine whether you deviated from your expectations or not. Maybe your business requires immediate corrective action. You can start cutting expenses, looking for better marketing tactics, revamping your sales strategy or exploring ways to make your cash last. It is possible only if you have and maintain a plan that gives you an advance warning.
Your understanding of the risks improves with experience. Even if everything is going as expected, revising your plan gives you the chance to find out whether the business landmines are where you thought they'd be. You can predict most business risks beforehand and keeping your plan's risk analysis current annuls risks before they happen.
You may also use a current plan as training tool. With the help of copies new employees understand how the company is put together and what expectations you have regarding its growth. Moreover, department heads in some companies are required to create their yearly plans aligned with the goals laid out in the general company plan.
Strategic planning off-site, good project planning and ongoing employee training may substitute a business plan in some way. But a business plan brings all these benefits together in one place. Just keep the plan current, and this document will help to run your business. | 
