Most maternity underwear tries to solve rolling by going higher — a thick band stretched over the whole bump. It works for some women and drives others mad, because that band is under constant tension as the bump grows and it presses in.
The V-cut does the opposite. It sits below the bump entirely, so the fabric isn't fighting your body to stay in place. There's nothing for the bump to push down. If you've found high-waist maternity bands squeezing or too warm, this is the alternative.