as an alternative to a text editor, it's an attractive nuisance. Yes, you can try things out and see the results instantly, AND you can save it, edit, rerun, etc; the cost is that debugging becomes a nightmare.
Remember that Jupyter has a pretty nice text editor (with syntax highlighting! but no autocomplete or discovery... yet), and there's nothing stopping you from teaching a student how to write a .py file in the Jupyter interface and then import it in a cell. And then showing them how they can do the same thing with ANY old text editor.