Performance issues are caused by much more than just should-update equality checks. There is a performance hit to re-rendering components due to updating the virtual DOM (which is a no-op in the case of pure components) and any logic required to calculate a re-render. If your render method takes 5 seconds to run, a PureComponent’s
shouldComponentUpdate is signficantly faster than that same component’s
render, and passing the same function reference will shave 5 seconds off its re-render time.