One of the core requirements of the type hints design is that they don't affect the Python language.

You can still write python programs without them.

You can add them only partially.

You can also add them later.

Python stays Python.

MonkeyType lets you take a code base that is untyped, or partially typed, for historical or because it was not worth it at the time, and turn it into a fully typed project quickly.

It makes the transition between the exploration phase into the industrial phase much easier.

For me, it's kinda fantastic to be able to fiddle with a design, changing my mind again and again, without having to fight the type system, then once things are settled, add an additional safety net on top.

It's also very reassuring knowing I can just hack things, knowing that later on, if I want to take it to the next level, I have the option to change my mind about type hints.