Imagine you're building a desktop application that does something like take a bunch of sensors from an attached serial port device and displays configuration of

Imagine you're building a desktop application that does something like take a bunch of sensors from an attached serial port device and displays configuration of them + a table of their values updating in real time. You wouldn't create every GUI element from scratch. You'd use the built-in Windows components (these sorts of apps are almost always windows-exclusive). Now imagine you're building a web app that does the same thing, except now it's hosted on the embedded system and you get to it via web browser. You're going to want it to behave like a desktop application. Adopting client-side GUI frameworks like ExtJS was so common you wouldn't think twice about it. The reusable components make it much closer to a desktop application than a website. If I were still building applications like that, I think I would still use ExtJS, warts and all. It's perfect for table-and-tree-driven application. Nowadays, if I want to build SPAs, I use AngularJS. It's hard to overestimate just how much of a revelation that kind of client-side framework is. TL;DR - In industry you often can't keep much server side. Instead you have to talk to lots of services and APIs directly from the browser. Additionally, you may need standardized GUI components that are familiar to people who only use desktop programs for the most part. Those two areas are admirably served by client-side frameworks like AngularJS in the first instance and ExtJS in the latter.