Or simply you misplace your wallet. Then you have to make the decision of how much you're willing to risk in taking out of your "totally safe" under-the-mattre

Or simply you misplace your wallet. Then you have to make the decision of how much you're willing to risk in taking out of your "totally safe" under-the-mattress stash each day, and that runs into inconvenience of if too high you lost a lot after a few beers on a Friday night, if too small you can't buy everything you wanted in the spur of the moment.