Estimates are useless as a measure of how well an engineer is performing. How far he is ahead or behind schedule only indicates the extent to which he was able to get away with padding his estimate in the first place.
That said, estimates ARE very valuable when you have a complex set of interlocking projects and resources that can be tasked in different places. This is especially true if external pressure require that a project be done on an exact date.
To take an extreme example, if the launch window for Europa is at a known date, the spacecraft firmware must be fully tested and installed by that date. Working backwards that says when the first version must be ready. The estimate helps decide what resources should be applied, and later it lets you know if you are so far behind that you need to change the launch date to the next window (over a year away). That affects budget etc.
At SLAC we have complex projects that require the work of lots of people to all come together. This results in very rigid schedules - There is typically a 2 month window for major upgrades, if you miss it, you wait a year. If someone working for me doesn't like doing estimates, I basically say "we need a guess. I can guess or you can, but since you are doing the work, your guess will be better than mine".