I think that dreaming is the only reason for sleep. Other than that, sleep has almost no importance or significance. Lucid dreams are dreams in which you know that you are dreaming, and so you can control yourself and tell yourself what to do. Lately I've been testing out how to get myself to dream of certain things, and I find that if I think about things before I sleep, or watch a movie before I sleep, I will most likely dream about it. Like 2 days ago I watched Harry Potter, and the same night I dreamt I was in Harry Potter. Such dreams are really fun to play around with because you can live your fantasy (don't be sick and perverted).
Another method that I find works is when I take naps. Usually my naps are like 15 minutes long, but I dream like immediately, and so I don't really fall asleep, but rather just dream. And within these dreams I know I am sleeping, so I can wake up on whim. I suggest you all go try it out, cause it is pretty fun.