The Single Responsibility Principle (SRP) in React ensures that each component has one reason to change, promoting modular, maintainable, and understandable code. An "All-in-One Component" violates SRP by combining state management, API fetching, and rendering logic within a single component, leading to reusability issues.
To adhere to SRP, refactor by creating a custom hook (useFetchPosts) for fetching data, a PostCard component for rendering individual posts, and a PostList component to map and display those posts. The main component (PostPage) can now focus solely on data handling and rendering, enhancing separation of concerns, reusability, testability, and scalability.