Wasteful: Unused compute sitting around in some datacenter is on the first order less wasteful than having it using tons of electricity to run a random puzzle.

Wasteful: Unused compute sitting around in some datacenter is on the first order less wasteful than having it using tons of electricity to run a random puzzle. Less electricity usage. However, the second order effects may negate the effect i.e. miners instead buy up more units, which puts more pressure on manufacturing, which ends up using that extra electricity, and the energy waste is equal. Attacks: that's exactly what you would need to build a tool for. You need to prove that you sit around, and not just promising to sit around. It's a tough problem! Proof of Not Work.