As a Zumba Instructor you'll be providing tuition and advice to your students. If they unfortunately suffer a physical injury while doing Zumba at your class whilst under your supervision then there is a risk that you will get sued. 

If this happens your Professional Indemnity Insurance will cover you for up to $5,000,000 to help cover the costs involved in a claim. Having cover in place also gives reassurance to your customers that you are bona-fide and serious about your business