Comment by card_zero

Some numbers here: https://en.wikipedia.org/wiki/Tidal_power#Principle (last paragraph). Tidal energy is wasted by natural coastlines all the time, being converted into heat and erosion. If this effect is constant, it looks like the day gets longer by 7 minutes 12 seconds every 36.5 million years. (I calculated that because it's a 1% reduction in rotational energy.) Human extraction of tidal energy is much smaller than the energy wasted by tides acting on all the world's coastlines, I assume. To some extent it takes energy away from coastal erosion, which also seems fairly benign.