Think of a yoga strap as an extension of your arms. Like the yoga block, a strap is a tool used to assist the body in the physical practice of yoga, asana. As I said in my blog about the block, using props in yoga should not be looked at in a negative way. Think of props as an opportunity to expand your practice by giving you more options and choices in postures.
We use these straps to create length to improve reach and increase our range of motion. This in turn helps our practice in so many ways such as improving our flexibility and posture. Plus, using a strap correctly in our asana practice will help prevent injuries caused by overreaching.