Fundamentals, Cycles & Trends (FC & T's): Your plan, if done in advance and thoroughly, should provide and excellent foundation from which to work. Even the best plan still has to react to outside forces that will influence your best intentions. Identifying certain fundamentals, cycles and trends that may impact your company is a prudent way to being able to develop a contingency "plan B" in the event an outside force rears its head. A series of key FC & T's should be monitored throughout the year so that if required, your plan can react. Certain FC & T's may include wholesale pricing, weather, commodity markets or labor market impacts that are out of your control. In my opinion, developing contingency plans in advance for these outside forces at least gives you a fighting chance to react favorably.
For an online business, a detailed and in depth business plan is usually not necessary unless you are trying to combine your online business with a traditional business. For most online business startups, the detail involved with planning a traditional business is not required. However, it would still be beneficial to you if most of the topics were still covered, even if only briefly. Having a written plan in front of you will help you to focus on important aspects of the business.