What is the expected return of `useEffect` used for?

Question

In the React documentation for hooks they say:

\"This also allows you to handle out-of-order responses with a local variable inside the effect\"

Answer 1

//all imports
function mufunc(){
  useEffect(()=>{ 
    const a = addEventListner('mouse' , console.log('mouse moves') )  //it prints when 
                                                                      //mouse moves
    return ()=>{
      removeEventListner(a)  //whenever the component removes it will executes
    }
  } ,[])
}