Like anything else in business, a business plan should be judged good or bad not in a vacuum but in its business context with its specific business objective. Most of the online discussion about business plans is focused on business plans related to seeking investment, and I`m going to make the assumption in this answer that you are asking about those.
Are you still unsure whether a business plan is worth the time and investment? Can`t you just jump right into starting and running your business? You could, but you`ll be missing out on some key benefits that a business plan provides.
The best use of business plans starts with founders using plans to establish strategy, tactics, milestones, and (especially important) essential projections of sales, spending, headcount, startup costs, capital needs; it`s for the founders to know, first, what they plan to do.
You should know what you want to get out of your business upfront. Are you wanting to turn a side hustle into a full-time business? Trying to expand your team or launch an additional location? Knowing what you`re trying to accomplish, and having questions like these in mind, can help you develop your business plan specifically to reach these goals.
Things like: Could you grow faster with more money? What are your headcount assumptions? How much are you spending on marketing expenses? What are you assuming for payments and collections lags?
People who read your business plan will already know a little bit about your business because they read your executive summary. But this chapter is still hugely important because it`s where you expand on your initial overview, providing more details and answering additional questions that you won`t cover in the executive summary.