The Playstation 3 used to have Folding@Home that users could opt-in to. I've always thought that the cycles that crypto currencies burn for mining could be much better used for something like performing protein folding calculations (or something else beneficial) and mine some coin in the process.
Algorithms used for proof-of-work have to produce solutions that are very efficient to verify (it needs to be much more efficient to verify than to compute, and it also just needs to be very efficient to verify overall because every potential block processed by each node has one), it needs to have a smoothly adjustable difficulty factor, and if the solutions are economically valuable to anyone, it weakens the value of it as a proof-of-work algorithm because it can cause mining to be a much less level playing field and cause double-spend attacks to be more profitable.
Imagine a university gets a huge grant to run protein folding calculations, and the grant lets them do more than everyone else including miners: now they own >50% of the mining power of the cryptocurrency without making any investments intended toward mining and can now do 51% attacks at no added cost.
Or imagine someone with less than 50% of the mining power trying to do a double-spend attack: normally this is discouraged by the fact that double-spend attacks are probabilistic, and the attacker has to pay the full cost for doing the attack regardless of whether it's successful. But if the proof-of-works are valuable outside of their purpose within cryptocurrency as proof-of-works, then the attacker can re-coup some of the costs of their attack by selling the results of their proof-of-works. Double-spend attacks will then have higher benefits and may be profitable to attempt now.
Additionally, proof-of-work systems used by a decentralized cryptocurrency can't rely on a centrally-produced dataset. If the Folding@Home group produced workloads for the cryptocurrency miners to solve, then the group could construct fake workloads that they already knew the solutions to, and then secretly insta-mine those workloads themselves to earn mining fees or to do double-spend attacks on the network.
I think it's better for cryptocurrencies to instead focus on developing solutions that just don't need proof-of-work mining to happen at all, like proof-of-stake.
"Proof of useful work" has been attempted for a few things, including this. None have really taken off. I don't know all the difficulties involved super well, but sibling commenter seems on point.
Many of the attempts to use folding as proof-of-work for cryptocurrency devolve to: have some central authority keep track of how much work everyone does, then hand out coins as appropriate. And if you have a central trusted authority that can issue currency arbitrarily by fiat, you have very literally just reinvented fiat currency, in which case you might as well just create a normal mysql db instead and call it a day.
I disagree. I think centralized issuance with decentralized transaction is useful, because maybe you trust centralized authority not to abuse issueance, but do not trust it not to block transaction arbitrarily.
