This is not a tactical or strategic discussion. It is an entry on psychology. A mask is worn either to hide something you do not wish to show or present a false face. We all project masks everyday in many ways. How often is someone completely honest projecting themselves as they truly are? Often if a stranger approaches me and is very friendly I immediately feel quite wary and keep my guard up. Acting friendly is a mask we can project to influence others to do what we want. On the other hand smiling is often the sign of utter submission. Have you ever seen people wearing sunglasses indoors? Your eyes are very expressive so hiding them shuts off a lot of information and is also intimidating. We all know the stories about cops wearing their sunglasses at night.
For some the mask is necessary since they are not comfortable with whom they truly are and it can help them to better fit in with a group. To me it's very important to present yourself as you truly are. So finally we come to the original subject of the death mask. A death mask is created from a mold on a dead person's face to preserve their image. Blood Angels wear death masks to fill the enemy with fear.