Abstractions reduce coupling

Two components are coupled, when changing one necessitates a corresponding modification, or at least a re-verification, of the other.

Coupling components located together is a good thing. They are said to have high cohesion. But when components spread across the application are coupled to each other, changing one produces a ripple effect throughout the system, destabilizing it.

Abstractions provide a way to reduce the degree of coupling between the two components by hiding away the intricate details o component functionality. If and when a component changes, other parts remain unaffected.

Abstractions also help in improving testability because fake implementations can act as stand-ins while running tests instead of real infrastructure. They also help in retaining the focus on the domain model instead of worrying about implementation details.