Time reporting for technology professionals?

How do you feel about the concept of such time accounting for technology professionals? (e.g. compared to just reporting progress via e-mail or a progress reporting form.)

 I guess, this is one the easiest ways to track actual cost/effort estimates for any IT project, so best suited for IT professionals. Reporting progress via email or progress report form doesn’t necessarily do any cost/schedule performance monitoring. What is important here is the tracking of actual hours worked which can be consolidated and multiplied by the hourly rates to arrive at actual costs and then linking it to performance evaluations systems.

Another personal advantage of such systems is that it helps to keep track of the tasks which you performed and is a ready-made tool to show your manager what you did for a particular time period.