Volume - 200 cc. Because there's less air volume in the mask, you have to put less additional air into it to equalize the water pressure as you descend or to prevent mask squeeze. Easier to purge. For the same reason, it takes less puffing to purge it of water. Because it's physically smaller and sticks out less from your face, a low-volume mask is less likely to be kicked off by another diver's fin or ripped off in surf.
Corrective lenses can be thinner.
The closer a refractive lens is to your eye, the thinner it can be. Cons Large nose pocket. The vision in one eye will be blocked by the nose pocket when looking to the side. This can be a problem for divers with one eye weaker than the other who do not use corrective lenses, because the brain has to shift from one image to another. A single-lens mask with little or no nose pocket permits binocular vision to left and right.