Kill Six Billion Demons

Kille billion demons is a very well written and excellently drawn web comic that's been going for almost ten years nowitin. Fltter, the guests immediately get him in there, of course, of yemen. And i think a good place to start is why should you use demons in a story? Like, what do they add to a story that you can't get in other ways? If anyone has thoughts, I'd love to hear them.