For some spaces they can make sense. For bedrooms, etc, might not be the best idea. 2 hose units are better as well when it comes to efficiency.
Some of the classrooms in my building have portables due to window design (there are some students who require them due to their 504 accommodations), but they are loud and are not really designed for spaces that large (900 sq feet or so)
My sister uses some portables for her dog business, but only in work spaces.