In order to know "where to go" in your practicing, you need to define your goal first. Knowing what the end result should be will keep you on track and help you filter out things that are not priorities for you.
By keeping track of the time of the day that you're starting your daily practice routine, you can analyze your practice habits and increase productivity.
Your practice log book is essential for efficient and methodical practice. By tracking your practice and planning it ahead, you can design a perfect routine for yourself that produces results. Your practice log book is a "navigation system", your "road map" for a perfect daily practice session.