Full screen grab here
Sean McCormack's latest Lightroom video shows how to add a decorative border to a print. He's using the Print module's ability to overlay an image other than the identity plate.

I noticed the same feature when I was writing my Lightroom book, but didn't think of a decorative border. Instead I came up with a more prosaic application - adding a copyright symbol to contact sheets, using a transparent tif file for the symbol. You can see the full screen grab here.

Funny how people find completely different uses for things.