In college I had to keep a life log for about a week as part of a psychology class. It was a completely manual process (i.e. pencil and paper; this was quite a while ago), and I was supposed to log in as much detail as possible what I was doing throughout the day. At the end we were supposed to create categories from the log, and add up all the time spent in each activity.
The purpose was to find out how much time was really spent on each activity, rather than what we thought we did. It was an eye opening experience.
I did something similar back in university after reading about Sen. Bob Graham [0]. For a period of 6 months, I would write down every single action with place and people involved in a small notebook. At the end of the day and the week I would review it. It was really eye opening and allowed me to change some bad habits.
The purpose was to find out how much time was really spent on each activity, rather than what we thought we did. It was an eye opening experience.