One of the most common criticism to financial planning and forecasting is : What is the point of prepare extensive and detail plans if you know you will be going to miss it. This reason drives the frustration of analyst where they spend more time explaining differences, than analyzing new opportunities and the business it self. Arie de Gus in a seminal paper of the HBR explains that the main purpose of planning is play with numeric models for creating different scenarios, this play with numbers allows to confront the mental models of the Managers. These exercises will bring new questions and hence more scenarios, this iteration process is what creates value because not just allows to anticipate future plan with actions also and accelerate institutional learning that is the key point. So, the true and real purpose of effective planning is not making good plans in contrast is to change the mental models of the decision makers carry in their heads.
Do you ever think it this way? Is awesome what you learn of your business with the planning process because desafiante every moment your mind.