In which cases should a service layer be used in application architecture?

The service layer in an application architecture is used to organize business logic and separate it from implementation details such as data access or interaction with external services. It should be used when:

• You need to centralize business rules and logic to avoid code duplication.
• It is necessary to provide a unified interface for working with different data sources.
• Simplifying testing of business logic by separating it from UI and infrastructure.
• The application becomes complex, and a clear structure is needed for support and expansion.

For example, in an Android application, the service layer can handle data operations, calling repositories, and providing results to ViewModel without revealing implementation details.