If a world matrix and camera matrix are both identity matrices, can they be omitted?

This is a basic question about the need for world and camera space matrices when each are identity matrices. Can they be omitted when calculating a 2D projection? I'm pretty sure that they can, although I seem to be getting strange results when I try to project some 3D points whi开发者_运维知识库lst omitting them, I ask since this might be directly linked to another question:

Projecting a 3D point to 2D screen space using a perspective camera matrix

Multiplying a 3D point by an identity matrix will result in the same point (hum, by definition), so I see no need to apply them if you are sure they are identity.