I've had banks go technologically tits up and render my funds inaccessible for multiple days in the past. Card payments fucked, etc.

Has happened to more than one bank I've used, in more than one country.

I've also had a bank freeze my account temporarily (for over a week) because some risk algorithm somewhere thought fraud was occurring.

All those times, having a bunch of cash handy was very useful.

As for hard assets: they make a decent hedge against financial shithousery.

> Under what situation could that possibly be useful where all society hasn't collapsed?

In a natural disaster type situation it could easily be the difference between being able to get what you need stay put the whole time or running out of some supply you didn't think you'd need and having to evacuate half way through the follow-on mess and losing quite a bit to looters and/or the environment.

The other person who replied mentioned more mundane stuff.