Why is power factor such a meaningful quantity?
Looking at it from outside the box, a device with a power factor lower than unity causes power to be wasted in the distribution of the power between the generation and the device itself. That's assuming resistive losses in the wiring dominate, so the \$I^2R\$ losses are higher than the minimum for a given amount of real power that has to be delivered if there is a reactive component. If there is a lot of reactance, the related energy sloshes back and forth between generator and device each cycle, causing unnecessary losses along the way, and not actually transferring any average power to the devices. 

What goes on inside the device is another question altogether, but it certainly needs to receive at least the real power that it consumes (assuming no energy storage) to satisfy conservation of energy. 

So if you were designing, say, a large switchmode power supply, you would optimize the power conversion and regulation portion to minimize the losses in the supply (within all your other constraints), but would also likely add power factor correction so that the input current is minimized in normal operation, as much as practical, but certainly enough to meet any relevant standards.