This is directly addressed in the PEP [1] - the short of it is, without the `async` modifier if you have two functions:

   def important():
       await something()

   def something():
       # ... stuff ...
       await something_else()
       # ... more stuff ...

and you refactor `await something_else()` into a new method then you've changed the return type of `something` from `Awaitable[ReturnType]` to just `ReturnType` and `important` will break at run-time when it tries to `await something()`.

  [1]: https://www.python.org/dev/peps/pep-0492/#importance-of-async-keyword