I had the same question two years ago, why should I sacrifice myself with the task of tracking all the activities I done in a day?
The answer came to me when we started using TSP (Team Software Process) in the company I work on, I started with some resistance to the concept of tracking my time, mostly because my train of thought said:
1. If I track my time I will not have time to read the newspaper on my work and will be like a slave running with the clock every single day
2. If I start to track my time I will never be able to get out early just because I will be always late.
3. When you track your time you will have to report the time to your superior and he will ask you to finish all the tasks based on the task with less time.
4. If I track the "real" time spend on a task I will not be able to use "reserve times" (Contingency reserve or management reserves) and when the known unknowns occurs I will be working until 2 am.
etc etc... What I discovered after 6 months in this new team work was that:
1. When you record your time you have the tools to explain why you take X time into a task, and you could show your boss that you used your time well, but some unknown tasks (that I know now) are messing with your times. For example I discovered that 20% of my time was spend on activities not related to the project I was working on, for example, meetings, explanations, customer support, etc etc. With this new real times, you can predict the behavior of new projects, and create tasks that support your real work. If you don't track your time you will not have that valuable information. In addition you could reassign some tasks to somebody else in other to avoid these "not project" times affect your work.
2. In most of the new projects I don't need the reserve times, just need them when a task is really unknown, and we spend some time in proof of concepts in order to determine that time.
3. Now I can be in my house early, I can say "hey, I worked 8 hours straight and I will leave the office", before the time recording everybody saw me as "hey, why he is leaving early, did he really get into the office earlier or just worked less than the other parts of the team?"
4. If I put an estimated time in a project I've data that support why I will spend that time, no one will be able to change my times because I already know how much time I will spend on that kind of task (ok, it's true... not all the tasks are exactly the same, but now I have some idea of all the activities I should do in order to accomplish that)
What I encountered during this time is that the tools to track the time are not really good, that's why I created my own tool that I offer for free on http://d-jon.com I hope you use it and let me know what do you want from it. d-jon will be free forever, and I will create some other non-free tools (billing, team servers, chat tools, mobile versions, etc) around it that will bring some food to my family :D.
I'm working on d-jon beta 1.2 right now and It will have some cool features like the ones you could see in the following screenshots:
new log view that will let you know what was the tasks you work on each day
new time by date view that will let you group and know the times spend to each task every day.
And some other features that I will post in some other blog later.
If you have any comment about the tool, or the article, please drop me a line with your thoughts, I will create a repository of "d-jon friends" and give away some versions of the new tools for free, also I will give a free android phone or iphone (I didn't decide that yet) to those of you that could say what do you like about d-jon and why do you think d-jon is useful.