Anticipating the future, especially in a fantasy context is what daydreaming is all about. The young people are the ones who generally have more fantasies as compared to the older ones. Perhaps that explains why daydreaming becomes less frequent as and when you grow older. For instance, you may often find young people have power fantasies like how would it feel to be a superhero. With the increasing age, people tend to loose these fantasies and so their daydreams also become less frequent.
You will forget what you were doing when you daydream
Research shows that people tend to forget what they were doing before the daydream if they are daydreaming about the past. How much you forget will depend on the type of daydream. For instance, the further back in time the daydream reaches, bigger is the forgetting effect. Besides the time factor, it also depends on the physical aspect. If you are daydreaming about vacation in abroad, you will forget what you were doing much more compared to the daydream where you have went for vacation out of state. This happens because the trip abroad is very much out of the context and feels like you are mentally transported back there. This is of great importance for the people who rely a lot on memory like those involved in careers such as medicine.
People spend almost half of their waking hours daydreaming !