What is the significance of having a good night's sleep? Can it be substituted by anything else?

Sleep has been traditionally considered as very essential. our elders would always advise us on having at least eight hours of rest every night. But in today's super fast paced world where there one is always running out of time, sleep has become a casualty. It is considered as something which is expendable for the sake of other seemingly more important activity. The so called night culture seems to be in vogue. Why is it that humans have almost suddenly started ignoring the basic requirement of their bodies, namely a good night's sleep? One larger question that needs to be addressed in this regard is how long can we continue in this manner? Is there a substitute for a good night's sleep? I would be doing injustice to my own body if i continue writing any further! So here's wishing everybody out there a very Goodnight and sweet dreams.