It's not absolutely necessary but we do use it to help in same assanas. Specially when you need to stretch in a certain way that you have to reach your feet with your hands and pull, you put the belt around your feet and pull the belt instead.

This is just and example, cause mainly what it does is that it helps you to reach, works as an extension of your limbs when you don't have much flexibility.

Hope this comment was of some help to you.

Thanks for the info eu, it did help me out.

You're very welcome, glad I was of some help.

Just keep in mind: don't be ashamed to use whatever props you need to do your asanas. Time and practice will get you along way. One day without realizing you'll be reaching your feet with your own hands.

seek out an Iyengar teacher.. they are experts with props.

www.rickytranyoga.com