Great, if you want to run a Nintendo DS emulator, or have two tablets sellotaped together at the hinge and call it a "laptop".
Otherwise? I honestly can't see the point at all.
Is it really that hard in this day and age to make a thin tablet, that slots into the top of a laptop screen (behind the laptop screen itself). When docked, single screen and it charges up the second. When undocked, it's a wireless screen / tablet that connects to the laptop and acts as a second-screen. Or functions entirely independently. At least for a few hours.
Kids bothering you? Pull out the screen and let them use it while you use the laptop. At a presentation? Pull out the screen and use it as speaker's notes/input to the main laptop. Working on a train? Tuck the screen behind the laptop screen and let it charge from it. I could literally glue a tablet charging piece of plastic envelope to the back of a laptop screen, run a few wires for USB charging, and find some software to use a second computer as an extended monitor (Chromecast-esque), and hey-presto, same idea.
I honestly can't fathom "notches", the little application strip thingy on the new Macs, or any other similar nonsense. I never figured out that gaming keyboard that was OLED on every key either. But it seems to me that nobody ever does the obvious.
Hell, sell the second screen as a tablet in its own right and save all the "unique" manufacturing costs.