Kundalini yoga is one particular kind of yoga known for using these kinds of mudras or hand positions. If you find a good instructor (or good video yogi, Maya Fiennes is my favorite) he or she will explain what these hand positions are meant to stimulate. I’ve done a few of these without understanding why, so I found this article to be particularly helpful. The idea is the hand positions send a signal to the brain to directly impact certain areas of your body. Can’t hurt to try right? You might experience less anxiety, better sleep, better digestion, and many other benefits.
Here is the full article with video and explanations: