Planning the other way around

I was puzzled by issues of personal effectiveness, where a lot of attention is paid to planning. For me, planning my next day is not an easy task, but to fulfill this plan ... And then the thought came to me that planning is essentially a pre-moderation of my time, and, as you know, there is also post-moderation. The point is that it may turn out to be quite effective not planning the next day, but analyzing the previous one. Knowing how much time I spent on work, and how much I lounged, you can at least simply assess the degree of your own drinking ***** twa and after that take some measures. The very realization of this degree can give a serious impetus to further self-development.

There are 2 ways to implement it. Or we open a diary at the end of the day and record everything retroactively, or we carry a stopwatch (PDA, mobile).

I think as a first step towards improving our own effectiveness, this method can be effective. What do you think? Maybe something similar has already been invented / described (didn’t google much, for 6 in the morning)?