Here are some of my reasons -
A Sport - Makes you strong, participate, negotiate and anticipate. Interaction with people, working as a team, working towards goals are involved. Enjoying victories and accepting defeats is all part of the game of sport and the game of life.
A Language - A lesson of words, insight and influence of other cultures, different angles ad views towards life as a whole.
An Instrument - Music portrays - Melody, Harmony, Peace, Integrity, Charity,Genorosity, Kindness and being Human which the worl totally lacks as of today.
All of the above teaches you how to be a good person and teaches you how to live life and enjoy life. Enjoy every single moment on Planet Earth.