This section is from the book "How To Intepret Your Dreams", by An Unknown Author.
The brain receives stimuli from many different sources all day long. There are far too many stimuli for it to process. The mind prioritizes the stimuli and makes you aware of those that need immediate attention (the crying baby, the out-of-control car, your boss' request) so that you may act accordingly.
The stimuli that you are not consciously aware of are nevertheless noted by the brain, but on a subconscious level (the drip of the bathroom water faucet, the remark by a coworker at the water cooler while you were on the telephone).
Furthermore, you feel emotions all day. Some you acknowledge and act on (you say thank you and smile when you are complimented.) Some you repress or do not allow yourself to act on (you don't punch your boss in the nose when he tells you the report you worked on for a week is no longer needed).
Traumatic experiences occur that you face (you call the police) or if it too painful, you deny them happening and send them deep into your subconscious (repression).
In addition to all these emotions and stimuli the brain must process daily, it also keeps your body functioning; it remembers names and faces; it allows you to talk and walk and chew gum (sometimes all at the same time); and performs numerous other activities that you take for granted.
You must admit — that's a lot to do. At night, when your body must rest, the mind continues working. When no longer called upon to type letters and do the grocery shopping, the brain concentrates on processing all of those subconscious stimuli and emotions (while still maintaining body temperature and breathing, etc).
This is why we dream. Only you are not awake to receive the signals at a conscious level — you can not hear or see or touch (at a conscious level) while you are sleeping. The brain must resort to other means to get the signals through to your conscious mind. This is why we dream the way we do.
The mind uses everything at its disposal (which is everything it has ever been exposed to) to get the message across. Simply put, dreaming is the minds way of processing all of the stimuli and emotions it has received during the day or repressed over time, so that you may act on them.
All in all, it's a pretty neat system. But unless you are remembering and making sense of your dreams, you are missing out on countless opportunities to learn about yourself and experience life to its fullest.
Even though we've addressed it before, it bears repeating. Why should you try and remember your dreams?