Preparing for the future is what a business plan is all about. So why is it listed here as a separate reason for having a business plan? Simply because a business plan positions you to continue your planning habit beyond the period covered by your first plan. You've already paid the up front cost in time and effort to assemble a plan. Refining it, revising it, and extending your projections beyond the original planning window will consume far less of your time in the future.
It's usually easier to do something the second time because the first time through you had to create a process. On subsequent attempts, you can follow or refine that process based on your experience. In effect, you set yourself up to continuously enhance your ability as a planner by having the plan available to you. Just as you refine the plan to reflect that interest rates weren't as high as you anticipated, you also learn to get better at making the assumptions and projections that make up the plan. There's nothing quite as educational as looking at material you've written in the past and finding errors that you would never make today.