You can skip the preview altogether if you have already read the book.
By photoreading and doing a quick postview you might discover that you know enough from the book already and futher activation really isn't necessary or specifically the section that you want more information from immediately jumps to mind.
Even with photoreading there may at times be books that you want to come back to later for more activation. Again since you already have some idea of what the book is about you can safely skip the preview and go straight for photoreading.
Alex
