The trouble with committing a date to ink
A wedding card is lovely and completely inflexible. The moment it is printed, the information on it is frozen, so if a second venue appears, the arrival time shifts, or the parking changes, the cards already in hands are quietly wrong. You then carry the correction yourself, explaining over the phone what the paper should have said.
A small QR on that card lifts the burden without losing the keepsake. The card holds the stable facts and points at the changing ones. A guest scans it and opens the current version of the day, and if a detail moves next month, the card in the drawer reads correctly still, because the card never claimed to be the final word.