PHP - Duda sobre sesiones PHP

<?php

require_once ('../conexion.php');

if ((isset($_GET['cerrar'])) && ($_GET['cerrar']=="si")){

	  //to fully log out a visitor we need to clear the session varialbles

	  $_SESSION['iduser'] = NULL;

	  $_SESSION['nombreuser'] = NULL;

	  unset($_SESSION['iduser']);

	  unset($_SESSION['nombreuser']);

	  $logoutGoTo = "http://localhost/mks/";

	   header("Location: $logoutGoTo");

	   exit;

}

?>