The main reason it is important in my mind is that it affects the oversight of the removal of pax. The person who knows they are in the gun if it gets ugly will run fairly close oversight of the operation, ( it makes them more likely to instruct a security officer on the tone of the operation), if nobody feels like it is on their shoulders then things are more likely to slip into undesirable territory.
Legal responsibility has a knack of making people diligent.