Desktop replacement for pen based workflows, like drawing, designing diagrams, architecture sketches, UI mockups,...
When coupled with keyboard, office like workflows, coupled with the pen to do the drawings instead of trying to use the mouse as pencil since many users have done during the last couple of decades.
Programming on the go with environments like Playgrounds, Pythonista, Continuous, Shaderific.
I could read my shitter news on any device with a screen, as well as control my smart home.