Purpose of a music promo video

1) To promote and publicise
2) To make money and increase sales

Synergy
The music video exists as a strand of multimedia campaigning. This is a way for the song to be promoted. The music industry as a whole is a relationship with a number of varied media:

• Radio
• Tv 
• Print media 
• New media
• Internet

There is often a sense of synergy across a number of platform, for example a film.

Love all round

Originally the song love is all around was performed by the Troggs, but only reached the top 50 on the charts. Then Wet Wet Wet made their own version of the song was made, this then reached the top chats in under three weeks which promoted the film Four Weddings and a Funeral, especially in the USA and continued to stay in the charts for 15 weeks. 

Four Weddings and a Funeral is a British Romantic film which had a unexpected success which could be down to the song promoted for it by Wet Wet Wet. The film cost was £3 million to make and made a worldwide box office of £245.7 million.