They live the business. They've probably forgotten more about the business then any consultant will ever know. If there is some important aspect of the business that the team identifies they don't understand then they will make it a strategic goal to gain that understanding. With a consensus on the specific need flows a commitment of resources and attention to an action plan that will gain the missing information in a timely manner. In the end the consultant goes home and the team implements.
Planning is an overhead function.
True, albeit an essential one. The best way to manage an overhead function is determine ahead of time how much time you are going to invest in it and then make sure everyone makes the best use of that time budget. As much planning as you do you can always do more yet nothing happens until you stop planning and take action. Balance is the key. We recommend devoting two intense, dedicated days annually to regenerating the plan.