Ask someone (including yourself) to think of productivity improvements and they hear you asking
How could you get more done in the same amount of time?
Not very motivating.
How could you get your work done in fewer hours per day?
They may not perceive a big personal gain in getting 10% more done per day, but they might perceive a big personal gain in spending 10% less time per day working.
Of course, if you’re just being manipulative, people will see through that soon enough. But if you sincerely want to pay for results instead of pay for time, this is a better to question to ask.