My wife knows mine and I know hers.
If I got run over by a bus and killed, at least she would have instant access to the funds in my account should she need them.
If I ever needed to answer the question 'does anyone else know your pin number' I'd simply say no as any fraudulent activity on my account wouldn't be my wife.
I also answer no to the question 'did anyone else have access to or pack your bags' despite my wife probably being the one who did the packing as she's not a terrorist or a drug smuggler.
I take it everyone using the arguement that it means they don't have to lie to their bank also apply the same principles to packing for holidays so they don't have to lie to the airport staff
Thinking about it when I was last stopped by a police officer and asked if I knew what speed I was doing. I said 30 (which was the speed limit) despite knowing full well I was doing close to 40.
Clearly I can't be trusted in any official capacity.