I found this technique great fun. I can remember using it with children when I was a teacher. The fact that you can't rub out makes it necessary to draw boldly and that is good for me, since my drawings can tend to be a bit "tight".
In this first drawing I was just getting my eye in and getting to know the chair. Some of the lines are a bit wonky but I quite like the effect. I love the shadowy ghost chair on the paper on the left.
I tried it again, to see if I could improve my drawing.
I think I have got the perspective a bit better in this one, but I started drawing too big and so there wasn't enough space to fit the complete chair in. I quite like it though.