Good post on Jeff Sutherland blog about the purpose of time sheets.
To sum it up:
- They demotivate developers
- 10-15% loss of productivity is the minimum
- Developers have to fake the time to fill them out properly
- Erroneous data is used for reporting and management makes bad decisions
- Customers are deceived
- They have nothing to do with quality code production
- They focus the whole organization on phony data instead of production
Even better, take a look at its graph. High quality work are on the X axis and number of hours worked during a week are on the Y axis. Even if your people work 20 hours a week, you get the same quality score as those putting 40 hours per week.