My neighbor of mine used to work as a bookie, letting people make illegal bets on sporting events. He said the toughest part about his business was the piles of cash he had to manage. He said once you take in around $500K USD (or something like that), you have so much physical cash that it prevents you from scaling. He needed to keep the cash on hand to pay the winners, and getting robbed would probably have been fatal. That gave me a new appreciation for digital banking.