Another aspect to this I’ve realized is that it can be a hassle to fish out three or four singles from your wallet, especially if they’re so new they’re kind of stuck together the way they do. Going back to my coffee scenario, if the bill is $3.22, and the customer has one $5-bill and four singles, I’m sure in many cases it’s much faster just to get the five out rather than the right number of singles. So singles get accumulated in wallets just as change accumulates in pockets, and you can end up with a wallet full of green that’s not enough to buy dinner.
Dollar bills may be light and silent, but they’re not always convenient to use.