Do not force your upper body to move forward if due to tightness in the hamstrings you cannot move forward. To overcome this problem sit on the edge of thickly folded blanket, which will also relieve the tension in the back of the legs and supports the pelvis while keeping spine straight.
Your abdomen rather than forehead should touch the chest. It is more important to lengthen your spine than bending forward as far as possible. Use exhalation to release the body further into the pose. If you cannot bend too far forward, use a bolster to support the upper body, since you can relax your upper body more. If you are a beginner, try raising and lowering your upper body two to three times and stretch away a little forward with each stretch. Keep your knees slightly bent and palms next to you on the floor on either side of the legs to support your upper body. Avoid if you have slipped discs or lower back problems.
Benefits to body parts - Stretches the back of the body especially spine and legs.
Other benefits - Refreshes if you are tired or ill.