What is the purpose of a music video?

There can be many purposes to a music video, some of which include:
-To show a song in more depth
-To add value to the song
-To tell a story
-To emphasise visual element
-To Promote the song
-To Gain interest in the artist and their other songs
-To entertain the audience
-To express meaning and emotion
-To cause controversy and publicity
-To increase the artists popularity and fanbase

Music videos are mainly used in order to promote the song and the artist. Due to a music video being created, the song can be played on a wider variety of media. The song itself will not only played on the radio, but on tv channels such as VIVA, and also possibly YouTube.
As the artist's song/video becomes popular people become interested in other songs/music video's the artist may have made and therefore promotes the artist's previous songs/music video's and gain higher interest in the artist.