For some consumers , for some people , when  they see a folding Smartphone which can unfold to a   15.6 inches screen size to  become a   15.6 inches  Tablet , they love it very much . The main reason I believe is  that for some people who want only one computing device , 15-inches screen size hits the sweetspot .  It's the minimum screen size to achieve the kind of usability , required in having only one computer ,  required in having only one machine .   And  that one machine ,  and that one computer ,  that one computing device could be  a  folding Smartphone (a  folding smartphone which can unfold into a  15.6 inches Tablet) which can serve as a  Laptop , which can serve as a  Tablet and which can serve as a  Smartphone .