But some people would start driving 6 ton vehicles because fuel is free. Limiting factor for crytpo mining would be only number of hardware you can get (provided crypto survives for so long). Some people would probably do the math and decide that thermal insulation is too expensive, and run heating/cooling on max. I could probably come up with more examples.

EDIT: from quick google query it looks like per day earth receives equivalent of yearly power consumption (not only electricity but also fuel). So we would need to x356 our energy consumption which is not that much unreasonable if you could have for example heated outdoor pool for free anywhere in the world.