I could not believe I read that.
Keep your money in a money clip that could be coughed up and your wallet/purse secured elsewhere. The reasoning being that most perps would take the quick money and the victim gets to keep their ID & credit cards.
I'm not saying that it's a good system, just that that's how some people do it.
Many years ago, I lived in an "urban" area. The social compact was that if you carried at least $20 for the mugger, and turned it over without a fuss, they weren't supposed to shoot you, and you shouldn't have to give them your wallet.
Fortunately, I never had to participate, but I never went out without a spare $20.