If estimates control how long you work, managers will tightly tune them so no one gets extra time off and occasionally people will be asked to stay back late because they didn’t meet the estimate that may have just been unfair. Any discussion around estimates will turn toxic when it’s an argument of how many hours people work.

Hours based work isn’t perfect but it means you can put in the average amount of effort and have consistent work hours without stressing over every task and if the estimate is perfectly accurate.