Question: why have a relationship. what is the purpose or benefit? 

Answer: to care about someone and have them care about you. Maybe love or a good friendship...............the purpose? don't you like good company and companionship?  the benefit. to feel the love and friendship. it can be very deep...it warms the soul and makes you feel alive inside
This question from the Yahoo Q&A forum is categorized in the topic: Science & Mathematics