I've been intrigued with the idea of installing Solus on a 32 GB USB 3.1 flash drive. That way, when I visit a friend as a Solus Evangelist, I can show it off without damaging what's on their computer.
Yeah, I could do that with just the Live USB key, but an installation on a larger flash drive would allow me to configure and save an interesting installation with real data. Think of "Show us your Solus."
The one time I tried it, though, the installer didn't recognize the USB device, even though it would be large enough and fast enough to do a credible job. Since then, I've read here that Solus isn't supposed to install on an external device. I don't know if that's because of an arbitrary decision or because some hardware issue prevents it.