at home I have a number of laptops. Any of them may become a shared laptop at any point in time with zero notice :) ( I already get enough grief for having the black original Das keyboard on my main desktop.)

At work there's less sharing but back when we were in the office, it happened. I also have two work provided laptops (one from my employer and one from client) which are heavily locked down.

Finally there's all the other keyboard manifestations in my life - on my work iphone and my personal android phone and the tablets and all the tv apps that pop up a keyboard to sign in etc.

Qwerty may be suboptimal but it's freaking everywhere.

For me, it somehow happens all the time. Helping out co-workers, friends or family. Using a different workstation than usual (we no longer have assigned desks). Sure, you can mentally "switch" layouts, but it's a pain.

Then there's the reverse: My PC at home - wife wants to check something quickly without turning on her PC.

Finally: I regularly use both a PC and a laptop. Depending on how weird you want the layout to get, there may not be a way to use it on the laptop. Schlepping an external keyboard around - nope, not practical.

The reverse is solved with a single button activating the default qwerty layout?

The direct with family is similar - you can have an extra layout installed

So the leaves even fewer cases where you really have to switch (but unfortunately not 0, no easy mechanisms to just easily switch to a some downloadable layout named after you on the fly at any computer)