[ohthehugemanate]

Maybe you missed the part where I explain how PMs translate to time for business planning. Yes that is absolutely necessary.

And yes it is an abstraction, which is the whole point.

Human brains are extremely bad and inconsistent at estimating time, and much better at estimating effort. So you abstract and let them estimate in the terms they're better at. Not to mention, the abstraction means you average in unpredictable disruptions like illness, windows updates, and other events. Abstracted unit estimates are demonstrated to be much more accurate than (not-abstracted) time estimates.