It's a mistake to think there is one purpose to fit all. You have to consider the book that you are about to PhotoRead. What is it you want and need to get out of this book? What do you plan to do with the information once you get it out of the book. Your purpose to read the plays easily was very specific to the book and class.
To read the Bio and Sociology material easily isn't the same thing for ultimate purpose. What you required from the books is more than just to read it easily. What do you need to know? How to you plan to apply that knowledge? That is your purpose.
Your purpose can change even as you activate a book. Your first purpose might be to PhotoRead the book to determine if there is anything you need to know from the book to apply to the class. Your second purpose with the second activation might be to activate a specific part of the book for xyz class.
As for PhotoReading books in the libray, go for it. Can be done at anytime if you have a purpose for doing it all the better.
Alex
