What are some surprising or lesser-known facts about how banks function and operate?

That Cash-in-Vault is money (cash) that the Bank has, but frowns upon. This is money that the bank cannot earn income on. This money is left by Customers who wait for a cheque to be cashed and then the very next day, empty their account out (hence it cannot be loaned out). On the ladder of love, Cash-in-Vault customer, occupies the lowest rung.