With Venmo/Square Cash, I find myself paying people via app more than anything. Forgot your wallet at lunch? Splitting up bar tabs? Our landlord wants a single check, and paying my roommate rent via Venmo removes all the pain of handing him a check (he was terrible at depositing them) without needing to carry around a few hundred dollars in cash every month. These apps have been available for years, and it's easy to get it set up to pay/deposit directly to/from a bank account, which makes transactions free. Cash is no longer the most convenient way to give friends money for me.
I'm also waiting for panhandlers to figure out Square is free, assuming they have a smartphone. "Sorry, no cash" stops being the end of the interaction if they start taking credit.