Comment by gnulinux
It's a literate programming tool. If you find literate programming useful (such as Donald Knuth's Latex) then you can write a Jupyter notebook, add text, add latex, titles, paragraphs, explanations, stories and attach code too. Then, you can just run it. I know that this sounds pretty rare but this is mostly how I write code (not in Jupyter notebook, I use Markdown instead and write code in a combination of Obsidian and Emacs). To me, code is just writing, there is no difference between prose, poetry, musical notation, or computer programming. They're just different languages that mean something to human beings and I think they're done best when they're treated like writing.
I have to disagree... Literate programming is still programming: it produces programs (but with an extra effort of writing documentation up-front).
Jupyter is a tool to do some exploratory interactive programming. Most notebooks I've seen in my life (probably thousands at this point) are worthless as complete programs. They are more akin to shell sessions, which, for the most part, I wouldn't care storing for later.
Of course, Jupyter notebooks aren't the same as shell sessions, and there's value in being able to re-run a notebook, but they are so bad at being programs, that there's a probably a number N in low two-digits, where if you expect to have to run a notebook more than N times, you are better off writing an actual program instead.