Why does React matter?
Redering is expensive and computation is cheaper
With React you can avoid direct DOM manipulation. Frequent DOM manipulations may cause unnecessary reflow and repaints for every manipulation. However, since React’s element tree reconciliation is a simple computation, it is cheaper than the rendering operation. If you can guarantee batch updates for frequent DOM manipulations, you will benefit from this over the cost of introducing virtual DOM. But on a static page, you’ll pay unnecessary costs. React benefits from web applications like Facebook.
Declarative UI development
All UI components in React are pure functions. Immutable data flows in one direction, and there are no side effects, so each component has only one outcome for its state. If you have to manage more than 100 components, it is a great advantage in predicting the actual screen to be rendered.
JSX is not just a pretty grammar that helps you develop declarative UI,
React.createElement( ... ).
As to why this is an advantage,
you can take advantage of the many features provided by the IDE within JSX.