The difference wouldn't be small, it would be zero. Exactly zero. Banks are not deposit-restricted in making loans, mortgages included. Money is fungible; if you withdraw your deposit from a bank, and then buy a corporate bond for example, the company will deposit the cash to another bank (could be the same, doesn't matter), then the two banks will buy or sell the needed funds at the end of the day in the inter-bank market (banks with funding needs will buy the cash, those with excess funds will deposit them). Net result zero. From an accounting point of view, withdrawing your cash reduces the bank's balance sheet by reducing cash on the asset side and deposits on the liability side, and the end-of-day offsetting transaction will do the opposite, raise cash in the interbank market and increase liabilities accordingly. Bottom line, functionally you are making zero difference.