If you are writing a business plan to get a bank loan or because you`re asking angel investors or venture capitalists for funding, you must include the details of what you need in the executive summary.
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.
All business plans should be reviewed and revised at least monthly. The review should include looking for changed assumptions and analyzing plan vs actual results with management of the difference.
Likewise, your business plan should answer these questions during the short-term period, particularly one year; specifically, what your business`s goals are for the current year, and what is essential in order to make your first year a success.
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?
You can skip the executive summary (or greatly reduce it in scope) if you are writing an internal business plan that`s purely a strategic guide for your company. In that case, you can dispense with details about the management team, funding requirements, and traction, and instead treat the executive summary as an overview of the strategic direction of the company, to ensure that all team members are on the same page.