Not as odd as you think. Few rivers really lend themselves to flinging the same length of line through the entire run. Fish hold in structure where the current breaks or rises. I've seen videos of casting instructors discussing the concept of "spey casting" versus "spey fishing." I think Pan is describing spey fishing. I'm light years from being an expert, but I'll usually identify the parts of a run I think hold fish and fish only those parts, except perhaps when I am "warming up" at the start of the day.