it's almost same impact

as extension on their next visa application (maybe even worse) since the VO will look at how long your parents actually stay here and if your parent already lose their strong tie to China. So do not make your parents go back and forth so often. It will not help at all, just makes them tired. Just try to extend if you really want them to stay. Somebody got 2 more extensions. Always bring the approval notice of extension for next visa application.