To add a bit (I wrote this in response to a deleted comment):
The yocto build I'm currently working on takes about six hours to complete on my biggest machine. Yes, it's an incremental build, but warming up a laptop would require several days of 100% CPU :)
It's also not really possible to test locally, even a VM of the right architecture is insufficient without doing a bunch of work to make it match the target hardware.
Often you can build a quick little ad hoc thing that lets you test some piece of it locally, but sometimes it's too much work.
Frequently I need to compile test several dozen Linux kernel configurations with different cross compilers, each of which takes half an hour to run on the huge box.
I can't imagine doing any of this locally on a single laptop, I would get 1% as much done as I currently do.
I guess that's hard for me to understand... do you just not have to compile things? Or do you just not mind waiting?
No matter how exceptional the laptops are for laptops, a real computer plugged into a wall is always going to vastly outperform them...