The essence of time management is the following:
1. Decide what to do
2. Do it
These appear to be very simple steps at first glance. Even a child can do them. However, when we look at them through the lens of optimization, they become much more complicated. In order to optimize these steps, we must concern ourselves with identifying the "right" or the "best" way to complete each step. We can easily see that some decision-action combinations produce better results than others. So our question becomes, "What is the best action to take right now, and what is the best way to do it?"
Answering this question should be the main purpose behind any time management system. Yes, there are side benefits like getting organized, becoming more clear-headed, and reducing stress. But ultimately these benefits all contribute to the decision-action process. What will you do, and how will you do it?
When I first studied time management, I found that most of the existing literature was focused on step 2. There was a lot of emphasis on how to get things done. This is a fine model for employees whose tasks are given to them, but that's an industrial age model, and it doesn't suit knowledge workers today who have a lot more freedom in choosing their tasks and even their careers. If step 1 is done incorrectly, then it doesn't matter how well you do step 2. If you decide to do the wrong thing, it makes no difference how well you do it.