I fill in three different timesheets once a week. One tracks the number of days I've done for the agency I work through, another relates to a single project and is easy enough, but the third!

That's used for client billing, resource utilisation tracking, forecasting, MI & project budget calculations. Also apparently it's used in performance assessment (although I wouldn't know for certain). In order to be paid for the time one has been on site, one must book a minimum of 40 hours a week to projects in this third timesheet. All team meetings, administrative functions etc must be absorbed into projects. Waiting on dependencies must be booked to something, or one doesn't get paid for the unbooked period (calculated by and rounded up to half days).

It isn't popular.

Oh yes, and not completing it to accurately reflect your activity is a disciplinary offence (see 'team meetings & administrative functions etc' above and try to figure!).