Unneeded code ?

[LMCrashy]

Hi, I'm currently trying to implement this technique in my engine, and while trying to understand how it works, I've some trouble understanding this code:

   //subtract from camera pos 

    vertexOffset = normalize(objectSpaceCameraPos-vertexOffset);

    //then add the original projected world

    vertexOffset += projected;

    //remove position of vertex

    vertexOffset -= vertex.xyz;

    //add pivot

    vertexOffset += imposterPivotOffset;

If I comment the previous lines and later in the file, replace: imp.vertex.xyz += vertexOffset; by imp.vertex.xyz = vertexOffset; It looks like it gives exactly the same result. Am I missing something ?