Hoarding copper pennies is a benign form of investing in liquid hard assets. They would be useful in a hyperinflationary scenario if low-denomination currency became worthless and copper recyclers were willing to risk melting them down. The second-hand copper market may already tolerate lawlessness given the sharp rise in recent incidents of copper theft. All of those torn-out copper wires, pipes, and fixtures are going somewhere. There's a buyer for every seller. I'm disappointed that law enforcement agencies aren't staking out metal recycling centers.
Penny pinching is one thing; penny hoarding is a big thing. There can be too much of a good thing.
Nota bene: This author does hold a small amount of pennies, in a tin can at the world headquarters of Alfidi Capital. They are currency, not a spare store of metal. I typically drop a few into the hats of street musicians in San Francisco, especially if they're talented.