You have a physical copy of a document and you want to retrieve the latest digital copy? A QR code on the cover page or on the document footer works well from the printed copy.
You need to copy/transfer a tiny snippet of information from a computer to another device without relying on a computer network? Generate a QR code and scan it from the other device.
And there are other use case if you rely on URI scheme, such as crafting an email template that prefills the destination, the object of the message and the body, etc.
One of the potential issue is that they aren't digitally signed, so you cannot validate their integrity or origin so you need to be careful about what you scan in a public setting.