React 18 and beyond

Starting from React 18 all state updates are automatically batched. In this way, React groups multiple state updates into a single re-render for better performance.

So when you update your state, React always try to batch these updates in a group update, causing fewer render than setState calls. The behaviour is the same when using hooks.

You can read the very long explanation in the Automatic batching for React 18 announcement.

React 17 and below

In React 17 and below, only updates inside React event handlers are batched. Updates triggered from promises, setTimeout, native event handlers, or other events are not batched in React by default.