Memorise the PPL confuser and you won't go far wrong
I agree with FFF.
Though there are things that you will learn and forget, the point of the exams is to teach the knowledge that you will need as a pilot to operate an aircraft safely and efficiently. They are not just there for the sake of it.
If you want to go on to ATPL theory, a sound understanding of the PPL theory will be a advantage. The Trevor Thom books are the best in my opinion.