Is CRAMMING Really The Answer?

Exams are coming and the big question is : ARE YOU READY? We, students, oftentimes, CRAM. But is cramming really the answer for not preparing ahead? We are given all the time in the world to prepare ahead. But why don't we do it in advance? Why do we have to wait for the last minute to do things? Come to think of it. I know you know the answer to my question. :))