I mentioned the financial aspect of a plan earlier, so let me add this. Another fact about financials to consider: not all business activities are about making money. Point being, in most enterprises financial considerations are centric to the document. But there are some other considerations. For example, a few years ago I wrote a plan for a new subsidiary that was focused on developing an inventory of patents. The potential financial returns were years into the future. Those patents may or may not ever have commercial value. Another example is a non_profit enterprise that has need for a complete roadmap for growing their profile in a market, of which a marketing plan would be the centerpiece.
Location: Writing down the location of your business is very important. Locations with greater customer traffic usually cost more to buy or rent, but they require less spending for advertising to attract customers. This is especially true of retail businesses where traffic count and accessibility are critical. If an online business, you need to go into detail how you will attract customers to your website. General statements like "I will use Face Book ads and email marketing" will contribute almost nothing to helping your cause unless you have detailed statistical analysis of tests you have conducted or of another similar business you have been associated with. If you do not have any data upon which you reference your estimates, it could show lack of proper thought to the remainder of your business plan.