I'm glad I work for you, because I can keep you happy by just constantly going "is it done yet?" as fast as I can. Any time I spend not running around at full throttle is just wasting me as a resource / employee.

Yes, even CPUs (modern ones) use less energy when they aren't super busy. Then there is the small matter of resource allocation not being perfect so having one CPU hog usually means your system becomes sluggish, slowing more important tasks (even though their priority is set higher), wasting the human user's time, and causing frustration.