Comment by qbasic_forever

A lot of these dunder (double underscore) functions are useful for metaprogramming. Just kinda spitballing an idea but perhaps some code to generate a python object model based on the schema of a database would want to use this method. If your DB schema has some special way of defining subclass relationships (maybe a foreign key to another table) you might need to manually control when something is or isn't a subclass in python's object model based on the result of querying the DB schema.

In general metaprogramming is the kind of thing you probably don't and shouldn't reach for first, in fact it's usually more for libraries and tools vs. your production business logic. It can get difficult to reason about and pass the maintenance of code that heavily uses metaprogramming to other people unfamiliar with it.