The purpose of a music video

A music video has a number of reason to make a video for their song.

1. The video can promote the band or the song itself. (if the band or song are not selling very well they can make a music video in order to show that they are a decent band or a decent song.)
2. Advertisement (some songs will include products in them to advertise what they are selling.)
3. Appeal to a visual audience (a visual audience is a group of people who are entertained by a show.)
4. Express a persons emotion (some song will have a big impact on the artist and will cause deep emotions.)
5. Tells a story (there are certain song that will tell a story through the video.) 
6. Markets an image (artists like lady gaga will want to show off a certain image about themselves.)