While most of the values stored by your component will be directly represented in the user interface of your application, sometimes you’ll use a variable only for the mechanics of your app rather than for consumption by users. You may want to use setTimeout or setInterval as part of an animation, so you need to keep hold of the IDs they return. Or you may want to work with DOM form elements as uncontrolled inputs, so you need to keep hold of references to those elements. Either way, you may not need to display these values to the user, and so changing them shouldn’t automatically trigger a re-render.