In a post entitled The Value of Timesheets, PM Hut offers this, "The data being tracked by timesheets is used in several areas: for project costing/estimating future phases or projects; for the purpose of time management; and most importantly, for billing and payroll."My comment in full:

Using timesheets to measure doneness of your project is like using a smoke detector to measure the doneness of your toast, by the time the alarm goes off it is too late.In addition time spent is not costing because it is based on the faulty assumption that all hours are equal. We know this to be false, yet ignore it. It is like still saying "but what if we fall off" even though you know the Earth is now round.Lastly, more often than not, timesheets are lies. I have asked hundreds of professionals if they have ever falsified a timesheet (up or down by the way) and every single one has admitted that they have done so. In many cases, they say almost all of their timesheets have at least one falsehood. Folks do not put actual time time spent, they put what the believe is should be, sometime more, but more often less. To base future work on these figures is crazy.