Soften skin with surface blur

I learn this technique from my Photoshop course class a year ago. How we can use surface blur to soften people skin. In this free photoshop tutorial video lesson, Yanik Chauvin will show us how to do that. He use surface blur rather than normal gaussian blur. what's the different? just watch the video and you'll know why we better use surface blur rather than gaussian blur to softening the skin.