The purpose of the ambiguity is to keep engineers involved in the time estimates. Otherwise folks may naturally compare the visible portions of some new shiny t

The purpose of the ambiguity is to keep engineers involved in the time estimates. Otherwise folks may naturally compare the visible portions of some new shiny to previous old shinies, not realizing some massive, hidden differences. If they cut out the engineers then the estimates are guaranteed to be way off. Pointing and T-shirt sizing aren't meant to make planning impossible. Just impossible to do without involving the workers closest to the work. Directly using time units could work, yet in practice are too easily misinterpreted as more precise than they really are.