I am more familiar with Android apps, so I will use them as an example.
Say one is browsing the website and finds an interesting podcast. The website could have a button that generates a QRCode pointing to the podcast's webpage on podcastindex.org. Apps could then register a link handler for the domain and open the podcast page inside the app.
This makes it easier to subscribe. Instead of having to search for the podcast on the phone again you can just scan a QR Code.