They produce vibrations and can affect the chakras and aura, for better or for worse, so you'll need to practice and get the tones right, to help clean and bring in beneficial energy.
They can also help with magick, if you know what you are doing with them.
I personally don't have any, they're not something I feel I need but some people might benefit a lot from them so if you feel drawn to them, you can get some and post your experiences