> repairs
I've replaced a couple screens on laptops. It's a fair amount of work, and in the meantime your laptop is dead while you await the arrival of the new screen. I keep a spare monitor around, and when a monitor dies, I just switch to the spare, and order a new spare. The same for many components, like keyboards, etc. I can't afford my machine to be out of action for days.
When I buy a new desktop, I really just buy a new mobo, CPU, and graphics card. The rest I re-use from the old desktop. It makes such upgrades pretty cheap.
I think that would be CPU, motherboard and RAM. Graphics cards can be upgraded independently thanks to PCIe, which I often choose to do as they are in a price league of their own.
I'm sad CPU sockets change that often, I would like to stretch expenses a bit more, like using DDR3 for a little while before switching to DDR4. Unfortunately, when upgrading to the next generation, you pretty much have to upgrade those three at once. And Intel is way, way worse with that.
I hear that motherboard manufacturers lobby for new sockets...
I often have to take the laptop with me to do work in other locations which completely rules out how cumbersome it would be to do this with a desktop. It takes me less than five minutes to pop it off the dock and throw it in my backpack.
Not to mention how much of a pain in the ass it would be if I had both a desktop and a laptop, constantly having to synchronize the data between the two, and having to have multiple installations of the same software which may be difficult depending on EULA/licensing.
Performance is in the eye of the beholder. The system I have performs more than adequately for all the tasks that I require, I rarely have to wait on compiles for any significant amount of time, video renderings can take a while but that just gives me an opportunity to stretch my legs and take a break from the computer.
Commuting to work with just a disk drive worked fine for me when I worked in an office.
I'm just not attracted to the idea of having everything on my laptop, because of the significant risk of having it lost or stolen. When I use a laptop, I just put on it what I'll need, never any personal things.