The STATE in Ethereum refers to the current information or status of all
accounts and smart contracts, and is a representation of the CUMULATIVE outcomes
of all transactions and smart contract executions up to the current block.
It's dynamic and changes with every new block.
The HISTORY on Ethereum, on the other hand,
refers to the record of all transactions and blocks that have been processed and
confirmed on Ethereum since genesis. This includes details like transaction data,
block headers, receipts, etc.. The history is essentially a log of how the chain
has evolved over time and how the current state has been reached.
It's a comprehensive record but is not directly required for processing new transactions.
In a sense, where History Expiry has a clear tradeoff in archiving old data that will become less accessible, State Expiry has the potential to be strictly positive, since it would only remove state trie nodes that have become obsolete.