I don't understand completely the benefit of using oldState / prevState. In the tutorial the code was changed from this :

  const DeleteClick = (id) => {
    SetMylist(Elems.filter(Elem => id !== Elem.id))
  }

to this :

  const DeleteClick = (id) => {
    SetMylist(OldElems => {
      return OldElems.filter(Elem => id !== Elem.id)
    })
  }

The guy said in the tutorial that if we use oldState / prevState then we get the most recent ( updated ) version of the state variable.