Apart from the biological and scientific reasons, there is one reason, why sleep is itself so essential for us, as human beings.
If we trace some good success stories, we will always remember that they had already dreamed that they would be great one day. Dreams are always interpreted as our visual effects of our deep desires. There is nothing wrong with us at all.
For, such dreams always motivate us and, more so, when we are young. Such dreams propel us to do better, become more focused and also meet with far more real world experiences.
Dreams help us to rejuvenate ourselves. Some dreams like the ones where we imagine that we "should get there", it has always been proved, only help us to work harder, explore new avenues for success and so on. The most creative directors of any cinema, particularly in local Indian languages have always spoken about their dreams and what it taught them. Some of the most creative and unique films have always come from some Aha! moment, that might have been triggered through their dreams.
Sleep is one activity, where we loose our consciousness. Sleep is something so natural helps us to restore our energy as the most important resource. We tend to think that today is a great day and only great things can happen to us, in a "here and now" experience, at the end of a good, undisturbed sleep.
Some of the good requirements are: leading a very ethical and morally upright life, always think of doing only good to others, always getting the negative things out of our mind, eating relatively lesser during nights and drinking at least one liter of good water, and so on.
This is so because our sleep should be natural, and should not be an induced sleep.