During an open book test, students tend to believe that studying or memorizing is unnecessary because they "can just copy straight from the book."
This is a myth for several reasons. For example, exams might have a word limit, which means that you cannot copy all the information that the book presents. Instead, you have to select the most important points, which could take you a long time if you are not familiar with the topic.
Another reason is the fact that questions are sometimes worded in a way that is meant to determine whether you have analyzed the material. It might ask you to draw conclusions, or imagine alternative escenarios. You cannot obtain that information simply by copying.
Finally, sometimes the wording of books might be different from the wording of questions. If you have not understood the material previously, you might not be able to fully understand the book, or to see the connections between the book and the questions.
Therefore, it is always better to be prepared and know your material well, regardless of whether your exam is open book or not.
