Does it support me to get calm, and if so why?
If the practice is Samatha Bhavana, i.e. tranquility meditation, then any object on the body can potentially serve as an object to develop calmness. Most commonly used, is the area around the upper lip and the entrance of the nostrils. Here the breath has a smooth and silky feeling which is very conducive towards the development of concentration, calmness and tranquility.
You could also the feeling of the emptiness in the body after exhalation, as you mention, and then focus your attention on that feeling and use it to develop tranquility.
It might be a bit more difficult, since shortly after the lungs will again be filled with air after inhalation. This movement of the air through inhalation and exhalation might affect the tranquility and make the mind waver, if mindfulness is not strong.
If mindfulness on the other hand is strong, then it might not matter.