I have a desktop, but I could imagine a life with only a laptop. Sure, maybe 99% of my usage would be at one desk, but if I need that other 1%, I need a laptop. It's the desktop that's an optional nice-to-have. And not everyone can afford or wants to have two computers which are powerful enough to do what they need.
In reality, far more than 1% of my computer use happens away from the desk where my desktop is located. I'm guessing I'm not alone in that.
You still only need 1 powerful computer. Networks are so fast these days and we have stuff like Tailscale it’s pretty easy to use the laptop as a dumb terminal and do all your work still on the fast computer.
Completely depends on what you're doing. If you're working on GUI software for example, you need to run that on your local machine. This is much easier if you're compiling and running the software on the same machine.
Then there are non-development tasks, like 3D modelling or video editing.
Remote desktop is a kind of solution, but it's extremely sub par. Latency is not good unless you're on the same LAN in my experience.
In reality, far more than 1% of my computer use happens away from the desk where my desktop is located. I'm guessing I'm not alone in that.