It gives a huge benefit, and not doing it is why most django code is incomprehensible and slow.
No longer should anyone in their module directly do something to a model and save it. They should always go through a service in the module owning that model, that makes sure everything is done correctly. So services.py and selectors.py works as a public API for the module, while the models are internal. Avoids having lots of other apps/modules depending on your app's internals.
