Tasking developers with creating detailed estimates is a waste of time

>For many of us a dearly loved date has already been selected, which makes our estimation efforts really interesting as we endeavor to shove more and more "stuff" into that bag.

I've always wondered why we are asked to re-estimate with smaller estimates after the first round. The end result is always the same, either the scope is reduced or the date slips. Bothering with all that estimation work seems to be a pointless waste.