I understand the gap logic, although I've never heard of it before.
Unless your very very good at hanging lining/wallpaper, there's always a line.
Well it isn't so much as logic, in my day we always crosslined if we were to have left the smallest of gaps it would'nt have had any effect regarding the finish paper. Yet if we had overlaped the seams the end result would have been disaster.
I think that this was the point that the Tutor was trying to drum into us, It matters not really what type of paper you hang, if the seams are correctly butted the entire surface would be uniform. Of course regarding both lining paper and the reliefs such as the Glylptas, you will always be able to see the seam yet the surface should be uniform and if hung correctly the seams would be obliterated with the application of paint.
Dec
I still stand by my last bit.