The traditional measure of a bank's capacity is the loans that can be handled based on capital and on deposit levels. When loan demand is low, the excess funding capacity goes into securities. When loan demand is high, banks buy large Eurodollar deposits in the overnight market. In banks' role as financial intermediators, this approach is timeless.
But the balance sheet is no longer a complete explanation of a bank's capacity. Banks are turning into transaction and information processing institutions. Much of the value they provide to their customers is no longer a part of the balance sheet. This new value is measured in different ways such as accounts, transactions, accuracy, or quantity of information processed.