This is for Jupyter Notebook.
For the cases when you start with huge dataset, and want to generate dozens graphs and tables on the screen, each changeable interactively without data reload. And leave python interpreter running, so you can run more code if you have more questions. Oh, and do all the hard work on the cloud machine with hundred of gigs of RAM, while displaying the data on your laptop over slow internet link.
I have tried to implement those things by hand (intermediate state, HTML generation, shotgun plotting, pdb interaction), and it is a major pain.
Notebooks work great in this situation. There are some downsides -- like inability to ask filenames from user -- but those could be easily bypassed, as this article shows (my solution will be a user-created symlink btw, not an ini file)