I don't need it when cleaning my inbox. Or planning a sprint. I don't need it when conferencing. Or when designing an architecture. I don't need it when reviewing PRs, stepping through a debugger, poring through logs, deploying, running ansible or finding what config made that deploy fail.
I split my time as such. I can work on my laptop for a morning, then go home and plug into my large screen just fine. It actually helps me focus: multi-monitor = coding. Laptop only = other work.
Interesting how people work different. Would not like to dig through logs without 2 monitors (allows to have 4 different logs open). Same with debugging (having multiple source positions visible). Or deploying (watching logs/deployment progress). Reviewing PR (having spec side-by-side with code).
It could not imagine any task I could do in a park (besides playing with a dog ;) )...
I'm also an artist, not a programmer, so I don't need to fill my screen with a ton of text. Plus my tools are pretty much designed around regularly zooming in and out.
When I was young, I carried a little subnotebook with a 7.1" screen and really enjoyed it. Now I have to hold my phone at a certain exact distance, too close and it's burry, too far and it's blurry. I had to use the 13" work laptop for a few weeks without an external monitor and it was painful, the screen was small enough that I have to lean in to see the text, but then I am too close and so I have to squint. I could crank up the font size, but then the screen doesn't show very much. Having the 27" external monitor means that I can sit at a comfortable distance and crank the magnification up so that everything is legible.
Be careful. One day, this might happen to you too. :D