Right but if it's the same as a laptop why not just use a laptop?
The only things I can think of are you really want to keep all the data on your phone and don't want to use cloud sync solutions (Dropbox etc.), or you really want to save a couple of hundred dollars getting a (probably terrible) laptop without a motherboard. Not very compelling IMO.
Surely long term it'd be cost? A screen and a keyboard in a laptop shell should be a lot cheaper that a screen, a keyboard, RAM, SSD, fans etc in a laptop shell.
Those other parts of the laptop are cheap though. Sure not free, but chromebooks can be had new for just a few hundred $$$ (they don't need a fan either). If you want a fast laptop you need to spend a lot of money, but a fast laptop has the ability to have better RAM, SSDs and such than your phone because there is more space in that form factor and so if you want fast you are back to laptop while if you don't need fast your laptop is cheap.
The only things I can think of are you really want to keep all the data on your phone and don't want to use cloud sync solutions (Dropbox etc.), or you really want to save a couple of hundred dollars getting a (probably terrible) laptop without a motherboard. Not very compelling IMO.