The ND Filter creates a darkening of the entire image, allowing you to photograph with a wider aperture or slower shutter speed than normally required. By slowing your exposure time or increasing your aperture, you are able to control the depth of field and convey movement in your images.
By using neutral density filters the camera is vulnerable to infrared light which will cast the unwanted red color to the photos when shooting at a small aperture. The added the infrared protection coating layer to this filter which helps to eliminate the infrared light through the lens to bring back the natural color.
The ND32000 (15 Stop) is widely used to capture extreme long exposure images (usually 3-6 mins in daylight), to create effects like cloud movement or cloud softening.