Like Johanna, I believe that time is better spent adding value, rather than producing estimates that are consistently wrong. The post leads off with a humorous and all-to-common conversation that highlights the problem with up front estimates:
Have you been able to [provide a perfect estimate] before?
Do you think you can get a perfect estimate this time?
Then why would you spend your time doing an estimate instead of producing something, learning from that and bettering your gross estimate?
Because my manager needs to know when the project will be done!