The hard gradation is perfect for horizons, or any hard transition between the sky and land. These filters give great control over the exposure.
The soft gradation is ideal when there is no definite transition between sky and foreground, for instance woodland, mist & interiors.
The medium gradation is perfect to filter the sky with minimal impact on the land. Ideal when elements like rooftops and mountains protrude into the sky.
The very hard gradation is not available for the Seven5 System. These filters already have a tighter gradation for the smaller sensors and a very hard grad is not practical to produce.