Perhaps your company tracks time using time-tracking software that automatically compiles the time spent with various clients. But, even it is doesn't, it is important to track how much time various tasks take in project management.
Hard copies of timesheets are useful as well. If your company requires time away from the office, timesheets can help track the time and don't leave team members thinking "Oh yeah, how much time on that meeting did I spend?"
A sample timesheet is posted in the Media Gallery.