I think the developers wanted "the mouse to be your hand" and you could aim the gun with the mouse without also moving the viewport. I remember missing this asp

I think the developers wanted "the mouse to be your hand" and you could aim the gun with the mouse without also moving the viewport. I remember missing this aspect in later FPS games. This was reasonable thing to try out and this was partly developed before DOOM so how FPS games works wasn't settled yet. Actually this problem with moving your hand independent from viewport wasnt solved unitil Oculus Rift CV1 with its hand controllers.