"by default". You still have to use those manually.
One of the promises of switching from class-based components to function-based was supposed to be an automatically applied version of shouldComponentUpdate, which AFAIK was never fulfilled.
Not true. Even if you memoize all the values and props used, your component will still execute, generate vdom and go through reconciliation. You must use React.memo in addition to memorizing everything in order to completely prevent a no-op re-render.
