He keeps the flow of the game going. It's all a byproduct of his confidence. A lot of that quick movement of his feet is reading the plays. He doesn't beat himself by getting off balance, either. He's human, he's going to give up goals, but he's solid.
All lateral movement shows is the ability to read the play.
He's so good at that. When he moves and gets down on his knees into position, he doesn't lock himself up, either. He's always ready for a second shot. Some goalies lock up and they can't recover. I think that's why he handles the puck so much, to stay into the play.