Too little sleep over too long a time is associated with all sorts of nasty conditions, including headaches, depression, heart disease, diabetes, and just plain dying earlier.
During sleep, your brain erases the less important parts of memories and simultaneously strengthens areas that you need or want to remember.
As discussed on the videos, you should get at least twelve hours of sleep in every twenty-four hour period.
Sleep is designed to allow for snoring, which clears your sinuses but makes you sound like an asthmatic banshee.
If you go over what you are learning right before you take a nap or going to sleep for the evening, it will NOT increase the chance of you dreaming about it.