PoW is a bit like a betting system: you either find the block and get a big reward or you don't. The finality of a transaction is not guaranteed. It is probabilistic. It is possible that a larger chain could reverse a transaction included in a block mined, but the probability of this occurring decreases as more blocks are added.

PoUW is different from PoW in that it chooses the provider who best meets the service requirements. This prevents sprinting for blocks. Providers are paid according to their hardware specifications. Miners are encouraged, due to the high payout volatility that is caused by the lottery-effect of miner payouts. To reduce this volatility, they can group together or form centrally directed pools.

The environmental impact of centralization is significant. The International Energy Agency reports that data centers are responsible for 0.3% worldwide CO2 emissions. They also use around 200 terawatt hours (TWh), or about 1% of global electricity demand.

It is also expensive to concentrate all computing power into a single site. PoW transactions consume a large amount of energy. The transaction fee must be high enough that it covers the cost.