This video teaches you how to do the binding parry against Hangetort, and why keeping your whole body behind your blade is important.

Binding Parries are for dealing with the likely crossing of swords. The goal is to catch your opponent's blade and get into a good position to counter-attack. Although passive displacement is not really what you should do in a fight, it is not always possible to avoid it. So these exercises are meant to teach you to bind/cross swords to your vantage.