Drawbacks of a business plan
Problems arise if the plan is too rigid; it is better to make it flexible, so that you are prepared for what to do if sales are poor (or unexpectedly high)
Many entrepreneurs have the whole plan in their head, not on paper
Plans based on high sales will include lots of staff to meet the demand; risks are lower if the business starts with a low-cost/low-sales expectation
Business success is often about people, not paper. An over-focus on a perfect plan may mean too little time is spent visiting suppliers or talking to shoppers