PhotoReading a book, multiple times it is useful for where one benefits from repetition. This is particularly the case in language learning, and often textbooks.
For most other books once is enough. However, if you are having difficulty activating, you might find it useful to PhotoRead the book, again. This is a good idea when you are learning something that is new, that you are not confident in, or have difficulty with in general.
Two students in my classes are usually recommend PhotoReading that textbooks for their classes daily at the beginning of term or semester for 2 to 4 weeks. Then the classroom discussion can become the activation. They often find it easier to follow the lectures and class as a result of PhotoReading their textbooks.
Playing with it, see what you get and think, what happens if?
AlexK