While I don't personally do a lot of work from a tablet, the option of a keyboard has always been appealing to me. I'll occasionally use my tablet to take notes for whatever review I'm working on at the time, pen a quick email, or some other third thing that I can't think of right now. For anything more than a short sentence or two, the software keyboard just doesn't cut it for me.
Hands-On With Google's Official Nexus 9 Keyboard Folio: A Great Case, Subpar Keyboard was written by the awesome team at Android Police.