When I was studying at university there was a rumour that one of the dons had scraped through their fourth-year exams despite barely attending lectures, because he had a photographic memory and just so happened to leaf through a book containing a required proof, the night before the exam. That gave him enough points despite not necessarily understanding what he was writing.
Obviously very few students have that sort of memory, but it's not necessarily fair to give advantage to those like me who can simply remember things more easily.