Ahem........a little "engineering education" and one of the very first questions that I have asked in any of my mechanical engineering classes:

"If you shut the supply flow off, be it hydraulic (water, oil, etc.) or gaseous (air, etc.) what results will you see concerning the pumping medium (the pump, the blower motors)? How does squelching the supply affect the motor, in other words?
Guess what, class. It takes less energy to pump (or blow) 50GPM (or 50 cu ft) than it does to pump or blow twice that amount.
Don't believe me, take an Amprobe to your central air furnace/ac with a clean filter and with a dirty fulter.