Doing line work is always relaxing. I did this on iPad. At first I used the pencil brush to sketch then retraced it with pen brush on a different layer. But I soon found it to be restricting and stressful. Man, that feeling when I missed the line as in tracing not directly on top of the pencil line!... urggh, undo, undo, undo. Yes I'm OCD that way. So in order for me to stay sane and not go nuts, I deleted everything and started from scratch using a pen brush straight away. It did the trick. Loved how free I felt and not doing a double work is always a plus.