Planning encompasses defining your departmental objectives or goals, establishing an overall strategy for achieving these goals, and developing a comprehensive hierarchy of plans to integrate and coordinate activities. It is concerned, then, with ends (what is to be done) as well as with means (how it is to be done).
Planning is very important if we are to develop a clear sense of what we wish to achieve and how we hope to get there. We must plan to ensure that we have the necessary resources (people, finance, time, etc.) and that they will be available when needed. Planning something thoroughly does not guarantee its success, but it certainly increases the chances that it will be successful.