Others of you can probably think of many other reasons why a single operating system blending Chrome and Android would be helpful, such as making tablets that work as notebooks, or notebooks that act like tablets.
Personally, this is the biggest obvious attraction: using the smartphone as the processor, docked to an external monitor or other tablet-sized screen.
For some applications, including content production, keyboards are a necessity and bigger screens very helpful. Sure, you could carry a tablet and external keyboard. You could carry a tablet and a PC, plus your smartphone. Many of us do.
But maybe having less to carry would be very useful.