To actually make something like this useful we need as many people using free email to also use PayPal or Google ‘Wallet’ as digital wallets.

Here are some of them:

-There’s nothing to lose if you’re not carrying it.
-In the event of loss, theft, or misuse there are certain protections you get with credit and debit cards.
-Using credit (and some debit) cards can provide rewards not obtained by using cash (frequent-flier or points cards….American Express ‘paid’ me over $300 this year for using my card last year, and I don’t carry a balance or pay any fees.)
-You can use a credit card in most any country without having to worry about that country’s currency (sure, there are fees. But there are fees to exchanging and trading physical currency as well.)
-Your transactions are automatically recorded (good for record keeping, bad for privacy) so you can track purchases and ‘remember’ where the heck your cash went.
-You can defer actual payments by 10-30 days using credit cards, or (not recommended) carry a balance if needed.
-You can’t run an open tab at a bar with cash.

So, while I’ll admit there are some disadvantages, they can be mitigated. Going cash-less happens to work very well for me.