Is calling IntersectionObserver.unobserve() strictly required?

Question

Recently I've been using Intersection Observers in React (16.4+) as follows:

const myRef = React.useRef(null);

React.useLayoutEffect(() => {
  const observer = new IntersectionObserver(
    doWork,
    { rootMargin: "0px 0px 0px 0px" }
  );

  observer.observe(myRef.current)
}, [])

Generally in React we're told to always return a cleanup function from our effect hooks if those hooks are setting up functions like window.addEventListener:

return () => window.removeEventListener('event', cb); // more cleanup

Should I be unobserve'ing myRef.current in a similar way? Or is that not strictly required in the same way it is for window event listeners?

I haven't found anything in the w3c spec regarding this, I've also been performance profiling my components and I haven't seen any negative results of not explicitly observing either.

Is there any consensus on this?