If you don 't and an object is being unserialized without its class definition being present, it will lose its class association and become an object of class stdClass without any functions available at all, that is, it will become quite useless.
Si vous l'oubliez et qu 'un tel objet est présent, il perdra sa classe, et deviendra un objet de classe stdClass sans aucune fonction, et donc, plutôt inutile.