Yeah I'm using Thinkpads as well.
@Scorpion Ghost they don't take up much space, they're 12" laptops and I've set up TightVNC (I used to use AnyDesk but TightVNC is so much better and faster) so I access them through my main PC 99% of the time. The main reason I started using laptops instead of getting 2-3 really powerful desktops is because I know someone who runs one of those businesses where they buy up used corporate laptops locally. From time to time, they buy a huge batch of laptops from some corporate office that's getting rid of old machines, and I get a very good deal from these guys to purchase the laptops in bulk before they resell them. It's extremely inexpensive, and I just install a really lightweight stripped windows OS and they're ready to go.
Regarding mouse/keyboard, again, I don't really need that, I'm accessing them through VNC. Don't need any KVM switches either. As I've mentioned before I got a custom perforated metal rack to hold the setup. And these machines are very economical (integrated graphics, low powered processers etc) when it comes to power usage, so my electrical bills don't go through the roof.
Yeah, this too. And I have fewer issues with concurrency, multithreading, memory leaks between scripts etc. I don't have to switch between a hundred browser instances in the scripts, coding is quick and easy. Basically this factor, coupled with the laptop seller source I have pretty much sealed the deal for me.