[rhdunn]

Cash is useful in cases where your phone/card isn't working. E.g. if your phone has run out of battery, you are in a location that has a poor signal, your account has been locked due to a suspicious/unusual transaction (even if legitimate), etc.

You don't need it all the time, just for emergencies.

[atq2119]

Systems you want to use in an emergency have a tendency to start failing when you don't exercise them regularly. That's my primary reason for using cash. Privacy is the second. The tactile sense for how much money I spend is the third.