Watts (and therefore KiloWatts) are amps x's voltage. Since motors (fridge compressor and furnace fan motors as examples) work on current, this current draw remains constant, but the voltage is higher, so you use more 'watts'. Hydro company makes more money, blah blah blah.
If memory serves me correctly, over at diyaudio, Nelson Pass conducted a small experiment. Using a Variac, he adjusted voltage on numerous systems. EVERYONE in the room preferred 'lower' voltage settings. 115v was one of the preferred settings. 120v was bad, and anything above this was horrid in comparison to 115v. YMMV
If memory serves me correctly, over at diyaudio, Nelson Pass conducted a small experiment. Using a Variac, he adjusted voltage on numerous systems. EVERYONE in the room preferred 'lower' voltage settings. 115v was one of the preferred settings. 120v was bad, and anything above this was horrid in comparison to 115v. YMMV