One people on the planet do this.
I'd bought the laptop first, got the MM because it's small and good for travel and using the top as a trackpad/scroller.
Then I bought an iMac and the 2nd MM came with it.
I'm pretty sure that I'm not that unusual.
> I'd sooner believe it's because they want you to buy 2 of them, so you can charge one while using the other.
We're discussing in this context. I still stand by the claim that there are probably around zero people on the planet that bought a second MM specifically to use it while the other one is charging.
I'm not doubting that there exists a group of people that happen to have acquired two MMs, however that came to be.
So when I get the "low battery warning" on the desktop MM, I put it on charge and use the other one for an hour while it recharges.