Citing source [1]
"To optimize your application structure, we propose breaking it into multiple modules:
- Service module for service declaration
- Directive module for directive declaration
- Filter module for filter declaration
- An application level module that depends on the above modules and contains initialization code.
This division allows for easier testing as it isolates the initialization code, making it simpler to ignore during testing. Additionally, tests can be more targeted by loading only relevant modules.
Keep in mind this is just a suggestion, so adjust it according to your specific requirements."
[1] http://docs.angularjs.org/guide/module