Timesheets are only wastage of paper for some, for some they are evidence of the work, for some they translate into money and for some they are just more things to talk about at meetings. I have had a love-hate relationship with them. I started by disliking them, but later realized what I could gain from them.
Timesheets were one of the bigger changes for me when I started on my own. Not that I did not keep them when I was working for someone else, but this time they did much more for me. Of course I did not understand this early on, it took some shocks and unknown factors to take help from them.
Today, most of my clients do not ask for them, I still keep them though, for myself. They act as a good record of my efficiency and also work as a great feedback on how I planned something and how it happened. In my opinion, the most unscientific aspect in software development is estimation. In spite of hundreds of tools and thousands of formulae it still is the most challenging equation to get right.
I use timesheets to verify the time and effort against what was estimated. It gives me a chance to think about the difference, and include that the next time I work on something similar. I can also calculate how much time do I spend in designing, coding, documentation and communication. Another very important thing in any process, whose significance I learnt from the Theory Of Constraints, was buffers. Buffers can be very effective to tackle with the unknown factors and unexpected events. Timesheets are a great place to record the buffers and their effectiveness.
I have been asked about what tools I use to maintain my timesheets. I have tried several tools, but they could never capture what I wanted and the way I wanted. I would in fact encourage every software professional to design his/her own timesheet and only then think about the tools. Keep it simple so that it is not a lot of effort to record the data and give some small amount of time to put in the details. I usually set the marks while working and add in the details at end of the day or on the next day.
If you dislike timesheets or think it is too much trouble to maintain them, it is quite possible that you are not using the right tools. Think about what you want to get from them and then start using tools. The data and how you want to see it matters more than the tools and the formats. Timesheets are useful, they are not only records, they can contribute a lot to your process.