Planning is deciding in advance what to do, how to do and by whom. It bridges the gap between 'where we are' and 'where we want to go'.
Yes, planning is worth huge costs as it is an important function of management, because of the following reasons:
It usually involves a lot of time, effort and cost of the managers. Collection of data, boardroom meetings, investigations and discussions with experts involve a lot of expenditure of the organisation. Sometimes, the cost incurred may not justify the benefit derived from the plans.