You can build pretty small, yet powerful, desktops these days. Well, you could until maybe a year ago...
The last desktop my employer sent me a few years back was literally 1/8th the size of the previous. Sans peripherals, it's a fair bit smaller than the laptop. Even with a small display, keyboard and mouse, not bad for portability. Now I'm not really "surfing the web in coffee shops" portable, more "I need this in the garage to do diagnostic shit on my car" or "prefer to 'CAD it' while field-measuring rather than sketch it by hand to draft later on", for context. I don't connect to public networks with it, ever.
Yes, well aware of Linux, and would if I could (have in the past for fun), but many of the programs I run require a Windows OS. Powerful CAD, 3D modeling, rendering and animation software is essentially non-existent in the Linux world. For the record, I despise M$ and have for a very long time, I think they make shit software, have shit business ethics (oxymoronic as that may be) and what some might call a dangerous monopoly...but I digress. The aforementioned laptop may well get some flavor of Linux in the near future.