More of a design pattern than use case. The best use case of nested function is a decorator. Other use cases can include limiting scope inside a function or splitting a function into sub inner functions if statements are repeated and recursion is not possible.

I will soon be writing a article on decorators. The are really useful. I use them most in Django for extending my views.

Also to define a Data Class in python a decorator is used.

Aagam Sheth Yes that would be great.

great article