I put one in my coffee machine, for example, so that I can turn it on/off remotely or on a schedule, as well as read the grinder value much more precisely (5V potentiometer) than the number the machine provides (1-45).
As mentioned in other comments, the Pico has two cores, so I’m actually running the small web server (for phone GUI) in a thread directly on the second core, meaning there’s never a time where I’m running code that could block web service. The grinder value gets updated 10x per second on the webpage via ajax, so it feels really responsive on your phone but doesn’t have to reload the page. I want to add a little oled to the coffee machine to show the output directly too. It’s a great little device.
I’ll be open sourcing the code in the future on GitHub once I’ve worked a few more issues out (my handle is CodeByMiles).
[1] https://docs.micropython.org/en/latest/library/_thread.html
That said, I've generally found the C SDK easier to work in. Copying large micropython libraries over USB to the Pico on OSX has been a massive headache.