Believe it depends on definition of 'economical'. What is your definition?
Quite sure...will speak for myself...the reason why higher cadence is used on a sustained basis is endurance. At lower cadence...call it mashing...my legs will lactate and I will slow down. So I can sustain higher speed at an optimal cadence.
And higher cadence isn't just about endurance, it is about speed. The top sprinters in the world near the finish of a race spin the cranks at 120-130 RPM to achieve maximum power.