Justification of usage of Blockchain by banks After learning a bit about Bitcoin and Blockchain Technology, I do not understand how any bank is going to use it.

My understanding is that the blockchain is useful in an environment of mistrust. In a closed system, like a bank, different nodes would be wasting computation if they used a blockchain with Proof-of-Work. If they just use the hash of previous blocks to verify the blockchain is never tempered with, without Proof-of-Work, can't any normal database do it much more time efficiently in a closed system (where all nodes belong to bank)?

What are the essential requirements for a problem to justify using the blockchain with and without Proof-of-Work?
Blockchains are best used when there are multiple entities that don't necessarily trust each other. So within one bank, a blockchain really isn't useful. However between bank transfers could use the blockchain. Right now, in order to send between banks, banks use centralized systems (ACH, SWIFT, etc) operated by a third party. With federated blockchains, they can remove most of that third party's involvement and thus save on fees and time. That's really the only good use case for banks using blockchains that I have heard of.