You're stil going to get to the same place at the same time as the other passengers.
Not in the same shape though.
It might not impact you much if you are going to one conference, but if you fly to multiple destinations within a week, it will build up. Your back/joint pain, stress level, lack of sleep will show. It might mean that you will save 5k on the boarding passes of your exec but then pay millions for the bad decision she makes.
It doesn't have to be multiple flights. Just one is enough - let's say you book a meeting a couple of hours after the plane lands, on a flight from Seattle to say, Singapore. That's a 19 hour flight.
I can tell you most people (ignoring jet lag) would need a day or so to recuperate and such. You really want said exec worrying about that pain in the back when discussing the finer points of a contract? Or being unable to sleep except in fits, completely dead tired and having to negotiate?
And sometimes schedule demands make the extra layaway day impossible. Enough so that companies that do send their employees on long transcontinental flights often allow the upgrade - a fit and refreshed individual is able to get to work immediately, versus wasting a day of hotel, salary, expenses, etc., just to save the plane ticket.