What is the purpose of a music promo video?

• The purpose of it to entertain the video
• promote the video/artist/album 
• advertisement
• Illustrates the song
• Appeals to a visual audience 
• expresses an individual emotions
• Tells a story
• Markets an image
• Persuades audience to buy CD/downloads
• Raises the audience awareness or profile of the artist group
• To make an artistic statement - e.g. Talking head - once in a lifetime.