Why is classical music useful?

Yesterday one of my students and I were discussing different styles of music. She originally learnt to play classical clarinet as a young girl. Then later on she learnt about how to play jazz. She then stopped playing for over 20 years. Now that she has started playing again, she is finding that all of her classical background has stuck in her memory, and while her theory is a little rusty, her muscle memory is still there. 

She started saying that she really loves Brazilian music and that recently she heard some really nice music played on the clarinet. So we started discussing different styles of music. I really believe that if you are going to learn an instrument, basic classical skills are a huge asset to understanding music. Then you can take what you know and develop further styles from there. But your fundamental technique is something that will always be with you and help you to 'control' your instrument sufficiently enough to perform any style. Then your homework becomes more about the stylistic approach than 'how do I play this instrument?'

I'm not saying that to learn an instrument you have to only play classical music in the beginning, but the classical approach to reading music, theory and instrument technique is what will give you a solid foundation to all other styles.