Gatekeeper, you misunderstand the physics of how simple centrifugal pumps work.
Doing what you're suggesting is actually more work on the pump than restricting the outflow. Seriously, put it on a watt-meter and check it out.
Common aquarium pumps actually run cooler, and at significantly lower wattage when throttled back a bit (on the output, always)
Agreed! They don't produce much pressure at all, so throttling them just means reducing the flow through them, and their power consumption is roughly proportional to the flow rate they are driving.