The best feature of photoreading is you ability to zero in on where you impulses guide you. This isn't just for dipping. Also for opening chapters, pages, sections of the book that answers the most important questions (to you) first. You build comprehension best buy building onto what you already know and what perks your curiosity. This most often means you don't necessarily want or need the information in the order that the author has pesented it (Novels usually, yes and even then not always).
This may mean that you superread a page without dipping and then later superread and dip that page because something layered the need for that information. Yes, it means you may even go back a couple of pages or activate the book backward. It means that you may superread some pages 2 to 8 (or more; it's allowed) times before you actually dip on anything on that page.
This is what is meant by building the comprehension or getting the book to gel through multiple activation passes.
The benefit is it uses your base knowledge to start building your comprehension and that is often not the same linear pattern the author has presented the chapters in.
So by asking yourself mind probing questions and considering your purpose you will be able to start anywhere in the book. After all you've photoread the thing in the authors sequence you and it's has already been recognised internally so you can now go directly to what you want and need to know consciously.
Bit like looking at a buffet without taking anything but quickly walking past everything to see what's there (photoread). Then activate by going directly to what you want to eat. In the eating you might discover it has given you an appertite for more and you are free to go back for more (multiple activation passes) or you found exactly what you wanted and had enough for now (the buffet will be there id you want more later).
Alex