Prior to the React.lazy() function, code splitting in large React applications was cumbersome. Code splitting is important for large applications because it reduces the size of the code bundles that are sent to the browser, which can dramatically improve the user experience. Some features of an application might never be used, which means that the code that implements those features is never delivered to the browser. This is a huge efficiency gain.
With the addition of React.lazy(), React acknowledges that code splitting and the user experience of waiting for pieces of the application to load are integral parts of the application, not an afterthought. By combining React.lazy() and the Suspense component, we get fine-grained control over how our app is split up and what happens while the user waits for it to load.
You can read more about code splitting here: https://reactjs.org/docs/code-splitting.html.
