If I can stash a small rig somewhere, then I can produce currency. This process doesn't require scale or major investment, so you could mine at a small enough scale to be below notice (See also: black markets). This seems like a viable way to save funds at a personal/family level.

Stashing of small to moderate currency against a low-quality government or mafia (via the conversion of electricity) seems like one good use case of currencies. If this isn't the case, it would be genuinely interesting to know why.