Machines is a 3rd party URI search engine. I'm not entirely sure if only one type of link will stand the test of time, but right now it seems like it could be helpful in keeping links that may be useful sometime in the far future.
My confusion right now comes from not knowing whether this is an index of articles that I've read and that have no place on any of my pages, or links that I believe could be useful in the future.
Either way, I'll figure it out. Hey, I may even add more types, like Netflix movies, and Spotify albums.