I am already a RN, but when I read your post, it took me back a ways to my old college days. I read the entire book of Pharmocology before starting my Pharm class because I heard the Professor was a tough cookie. I was told how he loved intimidating his students, so I wanted to prepare myself as much as possible for his class. He was a tough Professor, allowed no room for error, and didn't crack a smile the entire quarter I was in his class. He was even the one who wrote the Pharm book that the students had to purchase for his class. Talk about only wanting you to know HIS stuff and no one elses!
I received a 93% for the class, and once a student passed his class, he would then smile in their direction. He would even talk to you in the hallway in passing, but not before you passed his class. I know for a fact my reading his pharm book in its' entirety prior to the start of class familiarized me with his method and style of teaching which made all the difference grade-wise. So, if you feel in your gut that you should at least familiarize yourself with a certain textbook before class, then follow your gut feeling. Some students don't need to do this, and some feel better if they do. It's an individual choice, IMHO!