I think it was necroed by a Japanese Twitter addict(@tsutsuii) to display Twitter user icons without X on NetBSD/luna68k, then others started doing all sorts of unholy things with it from w3m with images to terminal-based RDP client.
There aren't a lot of "legitimate" use cases for now, I believe, but it's neat, and IMO an image mode extension for tty kind of makes it whole.
There are some fun things you can do with it like terminal image viewing, etc. The notcurses library uses it, some of their demo videos are really neat.