When you finish a practice session, what is your measure of success? Is it a matter of logging time, such that as long as you remained focused for 30 minutes, an hour, two hours, etc., you have completed a successful practice session? Or do you take a few minutes at the end of each practice to itemize passages rehearsed, tempos reached, technical issues addressed, and musical improvements made? Time spent is a requirement for musical growth, but it is not necessarily the best measure or indicator of it.
Consider exiting your front door and starting to walk. After an hour, where would you be? Depending on the initial direction chosen, evaluations and corrections made along the way, and the pace of your steps, the answer could vary widely. You could be at a favorite restaurant, a nearby shop, completely lost, or back on your front porch.
The same goes for your practice time. Failing to plan how you use that time and neglecting consistent evaluation can leave your musical growth at any number of places. Simply taking time after each practice session to identify what you’ve accomplished and plan what needs your attention the next day allows you to chart the course for your musical improvement and better know where you might arrive at the end of that phase of your musical journey.
How and where you make the notes and plans is completely up to you. Pencil and paper is fine, using a notebook or journal works great, or dictating your comments into the Notes app on your phone is perfectly acceptable. The only thing that is important is that you take time to identify your accomplishments, note areas for improvement, and plan for future efforts so that your growth is a matter of design rather than chance.