Dr. Candace B. Pert
One extremely important purpose of emotions from an evolutionary perspective is to help us decide what to remember and what to forget. The cavewoman who could remember which cave had the gentle guy who gave her food is more likely to be our foremother than the cave woman who confused it with the cave that held the killer bear. The emotion of love (or something resembling it) and the emotion of fear would help secure her memories.
My research has shown me that when emotions are expressed--which is to say that the biochemicals that are the substrate of emotion are flowing freely--all systems are united and made whole. When emotions are repressed, denied, not allowed to be whatever they may be, our network pathways get blocked, stopping the flow of the vital feel-good, unifying chemicals that run both our biology and our behavior.