John Voorhees at MacStories had this excellent article on Universal Control.
Personally I am not sure I will ever use it, thought it sounds very cool. The thing is I currently run 2 27″ monitors, an iMac Pro and a second display, and for an possible Mac Studio I have been considering moving up to 2 Ben Q 32″ displays. As it is, I have no room to fit my iPad on my desk and will have less with bigger monitors, still would be nice if I was running just one monitor.