As she brings down brings the bar down, we're trying to reach up to the bar with her chest...It's become a very common practice for athletes to lift their head off the bench, and unless you're very very mindful of it, then as the head comes up, the chest will often come down and the
chest will sort of retreat from the bar and that can cause a loss of upper back positioning. It can cause a loss of tension. It's also going to cause you to have to move the bar a further distance... You shouldn't need to lift your head...just be mindful of keeping your chest as high as possible throughout the lift.