Often the fantasy of breaking social taboos is erotic. Using fantasy or imagination, you can break away from the 'norm' for a while. In your thoughts and dreams, you can be more aggressive or more passive, in the setting of our choice. Sexual fantasies allow you to explore sexual desires, feelings, and behaviors without actually choosing to do them.
Whether or not a person has the ability or actual desire to do these is often secondary to the escape and joy that fantasy provides. Or they may dream about playing sports with a pro, having lunch with a senator, or even hooking up with a celebrity. People may daydream about being James Bond or a Charlie's Angel, a rock star, and/or a famous chef, for example. Fantasies are a great, safe way to explore exciting events and situations - that you may or may not actually want to do.