Comment by jeroenhd

The ability to store binary files comes to mind. PKCS12 certificate files and can't be turned human-readable without risking losing a flag or metadata or whatnot but the format is still widely used.

You could also use this as a basis for a printer+scanner system that exports and imports your system key store(s) automatically without having to risk OCR breaking your import.

Scanning a QR code is also just useful when it comes to entering long random strings. Although I agree that such a tool would do better outputting in plain text as well in case you need to enter it without a phone on hand, I think adding a QR code for loading the files quicker still makes sense.