The purpose of dreaming depends on the dreamer. There are many different kinds of dreams. Perhaps the greatest purpose of dreaming is to wake up as the dreamer.
Lucid dreams, where the dreamer wakes up in the dream and is able to take control of the dream, have a profound impact on the richness of dream life. Tonight, before you go to sleep, remind yourself to take control of your dream when you start dreaming. Do this each night until eventually you realise that you are dreaming while you are in the dream state. Instead of choosing to wake up at that moment, choose an activity you would like to participate in. Speak to a person that you cannot speak to in real life or even meditate. This is one of many powerful uses of your dream world. I would recommend keeping a dream diary and allowing your sleep to bring you new and exciting experiences.