Why is dependency injection considered a key aspect in software module design?

Dependency Injection (DI) allows for the separation of object creation from their usage, which increases modularity and testability of the code. Instead of the class creating its dependencies itself, they are passed to it from outside, making it easier to replace implementations and simplify maintenance.

For example, in Android, this helps easily swap implementations of repositories or services during testing without changing the class that uses them. DI promotes loose coupling of components and improves the scalability of the application.