Losing just one night of sleep can negatively affect your memory and ability to think for UP TO FOUR DAYS! That means that even one all-nighter could leave your brain utterly useless for most of the exam period.
Neuroscience has proven that we are only able to commit detailed facts (e.g. names, numbers, dates) to memory during deep sleep. Test subjects were better able to recall information learned the previous day after 8 hours of sleep. Deep sleep needs to take place within 12 hours of studying the information if this process is to take place.
In fact, you should study the hardest material right before you go to sleep because it will be easier for you to recall the next day.
A study from St. Lawrence University has shown that those who pull all-nighters average lower grades on their tests.
Sleep deprivation causes increased levels of the enzymes that cause your brain to "blank out" when you are trying to remember important information.
And seriously, when have you ever performed any task well on little to no sleep?