Very well written! Immutable objects are crucial when handling deeply nested data in JavaScript because they prevent unintended changes to nested properties, ensuring data integrity and predictability.

Giving an example: In React.js, using immutable objects can significantly improve performance by facilitating efficient updates through reference equality checks. For example, when updating state in React using immutable data structures like Immutable.js or immutability libraries, React can optimize rendering by comparing object references, reducing unnecessary re-renders of components and improving overall application performance.