Life is a marathon, not a sprint. If you stay up all weekend working or studying and ignoring your sleep, you're going to start the whole week off with a crash. If you throw caffeine or alcohol in to the mix and you only amplify the effects. Caffeine doesn't actually give you more energy it only prevents your body from realizing how tired it actually is. To me, caffeine is like borrowing energy on credit. You're borrowing energy from the future and with the crash you pay an interest penalty. Your energy also becomes inconsistent if you don't sleep on regular schedules and avoid caffeine. It's better to get a good night rest and start fresh in the morning than it is to stay up all night and work. The few extra hours you get out of it will not outweigh the lack of energy you feel throughout the next day.