Every KwH spent on useless calculations could be better spent heating a home, lighting a room, smelting some ore, or literally anything productive.
Incidentally, this overcapacity is why some estimate that half the global Bitcoin mining capacity is located in Sichuan and Yunan. Despite that, they just make a tiny dent in the wasted hydropower...
(And guess what - intermittency isn't a big deal for cryptomining / SETI/Folding@Home either!)