react.dev/docs/refactor/04-scaling-up.md

Scaling Up: Using Multiple Components

So far, we've looked at how to write a single component to display data and handle user input. Next let's examine one of React's finest features: composability.

Motivation: separation of concerns

By building modular components that reuse other components using well-definted interfaces, you get much of the same benefits that you get by using functions or classes. Specifically you can separate the different concerns of your app however you please simply by building new components. By building a custom component library for your application, you are expressing your UI in a way that best fits your domain.

Composition example

/** @jsx React.DOM */