The main use case for a block chain is to ensure that a ledger is valid and not tampered with. The reason we want public ledgers is to keep track of financial

The main use case for a block chain is to ensure that a ledger is valid and not tampered with. The reason we want public ledgers is to keep track of financial transactions securely. Why can't we just use a bank? At some level there needs to be security for the bank's database. Blockchains are generally considered the best way to do this. So when legacy financial databases are replaced in recent years blockchains are often considered. Public blockchains are even better because they ensure the validity of the overall system.