There are "Business Plans" (to persuade/impress lenders and investors), and then there are Business Plans: what are actually used to manage the business.
In an ideal world, the two are the same.
However, we don't live in an ideal world, so quite often, they can be very different.
Whether you're working with lenders/investors or not, if you have a business, you need a plan. Flying by the seat of the pants simply won't do. It's a sure recipe for misery and failure.
A credible business plan begins, believe it or not, from a Lifetime Savings Plan, continues through a personal budget, and culminates with the business plan itself. Once the budget is written, the business plan flows directly from it.
Every business plan is different; but usually, the budget is translated into a Break Even Analysis and Profit Plan, and flows from there, with as much elaboration as is necessary to work with the size, scope, details, and constituents of the business.