What is the purpose of music videos?

For my A2 level media project I have chosen the medium of producing a music video which will be accompanied by an original piece of music. First of all, I have researched on why music videos are assembled and how they are composed. The most vital reason is to sell. Music videos are short narratives which is accompanied by a piece of music which lasts the whole length of the song. It is used as a marketing tool to promote the sale of artists music recordings.