alt Hacker News30 years ago my boss at a large defense/aviation contractor told me estimating software projects was a very valuable skill, but all estimates were always wrong because they are simplifications and to keep that in mind -- his words.
Mainly they are useful to build belief and keep a direction towards the goal.
Models of any kind in whatever domain are necessarily always something less than reality. That is both their value and weakness.
So estimates are models. Less than reality. Therefore we should not expect them to be useful beyond 'plans are useless, but planning is indispensable' -- I think thats' Eisenhower.
I literally filled out TPS reports every week at this place down to the hour, breaking down internal project billing and customer billing. In order get the charge codes from the PM, you need to give them estimates. That was the main driver for estimates - convince the non-coders.