Nerd Alert: Why do we dream?

"Some scientists take the position that dreaming probably has no function. They feel that sleep, and within it REM sleep, have biological functions (though these are not totally established) and that dreaming is simply an epiphenomenon that is the mental activity that occurs during REM sleep. I do not believe this is the most fruitful approach to the study of dreaming. Would we be satisfied with the view that thinking has no function and is simply an epiphenomenon--the kind of mental activity that occurs when the brain is in the waking state?"