Pinterest is a catalogue — a code makes it a physical one
Pinterest is where people plan: a room, a wedding, a wardrobe, a menu. That makes it unusually well suited to physical placements, because the thing being planned is usually physical too. A code on a fabric swatch, a product insert or a shop sign takes someone from the object in their hand to the boards that show it in context.
Boards do the heavy lifting here. A profile code lets someone browse every board you keep, which is more useful than a single pin that may be seasonal. If you do want one board, use "Any link" and paste its URL.
Pinterest has its own in-app Pincode, but it needs Pinterest's camera to scan. A standard QR code is read by any phone, which matters when the person holding your catalogue doesn't have the app installed yet.
Everything happens in your browser. The QR encoder is built into this page, so your username is never sent to a server, nothing is logged, and there's no daily limit. The code is static — the link lives in the pattern itself, with no redirect service in the middle that can expire, start charging or go down.