Playlists or specific songs are often featured in books and movies for several reasons:

1. Set the Mood: Music can help to set the mood or tone of a scene. It can convey emotions that words alone may not fully express. For instance, an upbeat song can make a scene feel more lively, while a slow, sad song can make it feel more poignant.

2. Character Development: The type of music a character listens to can tell us a lot about their personality, tastes, and background. For example, a character who listens to classical music might be portrayed as sophisticated or intellectual, while a character who listens to rock might be portrayed as rebellious.

3. Cultural or Historical Context: Music can also provide cultural or historical context. For example, a movie set in the 1960s might feature songs from that era to help establish the setting.

4. Symbolism: Sometimes, the lyrics of a song can have symbolic significance in the context of the story. They can be used to foreshadow events, reveal character thoughts, or emphasize a theme.

5. Engagement: Finally, including popular songs or creating an original soundtrack can draw in audiences. People might be more likely to watch a movie or read a book if they know it features music by artists they like. It's also common for the soundtrack to be sold or streamed separately, providing an additional source of revenue and promotion.