The London hard fork will include EIP-1559, which lowers the amount of ETH miners receive. Currently, every time someone makes a transaction or interacts with a smart contract on Ethereum, they must decide on a fee, which is more or less a guessing game. To push through a transaction quickly, you can set a high fee, all but ensuring miners will include it in a block. If you lowball (intentionally or not), your transaction will likely wait until miners are less busy processing higher-paying transactions. Speed is important in several instances, including when trading upon Ethereum-based decentralized exchanges such as Uniswap, where token prices can swing rapidly; traders lose money if they wait.
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