You can read his reply to a graduate student question here. It clearly works for him, and there is some smart advice here. I think what is important – and I expect Graham would agree with this – is that you have to find out what works for you. I don’t work entirely like this, though there are some similarities in places. I think I’ve found a system that works for me. But so many people seem to be stuck in writing habits that are not productive for them there is a real value in advice posts like those Graham is so generous in providing.