What the postage was really paying for
You pay for the card, the envelope, the stamp, and then again in time. Someone has to address each one, and when a detail shifts you pay a fourth time, in the awkward messages where you explain what the printed card no longer says correctly. Paper is fixed the moment it leaves your hands, and the event is not.
An electronic invitation turns that around. It carries the whole plan in one page that guests open on the phone already in their pocket, and it stays open to correction. The map, the start time, the note about what to bring, all of it lives somewhere you can edit, so a change costs a single keystroke instead of a reprint and a round of apologies.