Yoga helps you gain flexibility in your hamstrings which can aide sports performance, limit injury, and allow for healthy posture. Because so much of yoga has to do with the orientation of the pelvis, the hamstrings are a key to going deeper in your asana practice. They will give you access to the pelvic positioning required in most postures. Your overall comfort and joy in yoga expands as these muscles loosen. And for those who have never tried yoga, it is a great reason to get started.
Your tight hamstrings not only keep you from touching your toes but could also be hurting your sports performance by limiting your range of motion and making you more prone to injuries such as tears, sprains, and strains. Most sports will benefit from flexible and strong hamstrings because they require short powerful bursts of running and movement.
To stretch the hamstrings try Adho Mukha Svanasana (Downward facing dog) aiming your heels back down onto the floor.
Hamstrings are related to the inability to have good posture while in a seated position, otherwise known as slouching. Flexible hamstrings allow the bowl of your pelvis to sit upright, rather than tip backwards. The tightness of your hamstrings can tip your pelvis posteriorly. This causes the natural curves in your spine to be compromised as flexion occurs. So not only does it look bad, but it could be causing you damage and discomfort as well.
If you have tight hamstrings try Sukhasana (easy pose) with enough blankets under you to get your hips above your knees. This will allow your spine to be erect and your head to sit comfortably above your shoulders.
There are plenty of postures in yoga that will help you gain hamstring flexibility. The ease developed from this flexibility will permeate through other areas of your life and inform day to day movements as well.