We initially automatically logged people in silently on Android by detecting their phone number, sending a verification SMS and intercepting it in the app. This was viewed as more spooky than good UX, so we had to reverse course a little and add another manual step in that case. But other little UX niceties remained, like extrapolating the customer’s name from the name of their iPhone (chances are you phone us called “[first name]’s iPhone”) to save them typing it in.
I think it would be quite difficult to manage a production system that lets people pay with cash but not log in, as it would be so easy for a single script kiddy to take all your restaurants offline by placing fake orders over and over.
You would be amazed (or maybe you wouldn’t) at how little business owners think about UX. We get so many requests to require a DOB before being allowed placing an order so they can send birthday messages to customers.
A nice summary of the state of affairs by UK comedian Michael McIntyre https://youtu.be/O5FeZti1cjs