The body takes the shape similar to a plough ( Hala in Sanskrit ). Also as the plough makes the hard ground soft, in this asana the veins are stretched which reduces the stiffness of the body.
In this asana the spine is stretched fully in a curve. It becomes more elastic and its overall functioning is improved. Like in Sarvangasana Jalandhar Bandha is performed and the same advantages are achieved.
All the muscles from toes to waist are also stretched helping improvement in the functioning of veins. This asana is also useful for gastric troubles, digestion problems.