When I last needed a paper receipt
The last time I needed a paper receipt was when a store detective stopped me AFTER leaving the supermarket. I didn't have any contraband and the problem was (eventually) sorted out. Eventually because he snatched my bag from me containing receipt, wallet, and the goods he alleged I stole so I had to involve the police. I now always pay with a card and keep my receipt in my wallet which will be in a pocket. I've not seen that store detective there ever since.
The moral is always have a paper receipt when you leave the store.