Nothing amazing, it's just an absolute minimum template for starting an Arduino shield in Eagle. You can download the files and start adding your design to the schematic, the headers are already in position and locked.
This means you don't have to download files from someone else's shield and delete everything, or try to copy the headers from the Arduino CAD files and have problems unlinking your schematic and PCB.
Yeah, I considered building an Eagle part, but there were a few serious problems with that approach. You can't remove headers if you want a shield that doesn't use all the headers, you can't remove text, you can't change the board outlines to whatever you want. He added some "package variants" to the library, but my approach offers the most flexibility.