The study design and previous VCAA exams are really important in knowing what to study and what you have to know and do to do well. Closely referring to the study design makes sure you don't waste heaps of time off topic and you don't miss anything that could be examined; it makes your study effective and efficient.
From my experience it's great in some subjects (HHD and Bio), not so great for Maths, and fairly useless in English/humanities. For good subjects, I'd make your own PDF/Word copy which just includes units 3/4 Key Knowledge. An effective way of studying is to take key knowledge dot points and write or speak and record all you can think of about that topic, with no notes. Then check afterwards using textbook/notes what you're missing, and make sure you learn that.
Also, every once in a while you could go over your document and highlight in green what you know really well, orange what needs some study, and red what really needs studying. It helps you target what you need most.