Anything graphical or interactive: maths, science, data, web, machine learning, etc. Interactive includes interactive widgets, but also almost any kind of exploratory programming.

Even stuff that's technically plain text is easier when you can display tables and other formatted text. E.g. I have a tiny little notebook that generates LaTeX code for a normal distribution table; it's a notebook because then I can display an HTML preview in a few lines of code.

Jupyter can't save interpreter state - that seems essentially impossible without adding state-saving and -loading code to every single library and dependency.