1. The shutter speed can be freely varied to suit the desired effect without changing the aperture, while maintaining the optimum iso. 2. A large aperture exposure can be used to create a bokeh background effect while maintaining the same shutter speed 3. Even with a shutter speed of 1/8000 second, a maximum aperture of F1.4 or F1.2 can lead to overexposure. The ND2-400 can easily eliminate overexposure in such cases, preserving highlight detail. *As with zoom lenses, the adjustable ND has a wider range of applications and is suitable for a wider range of scenarios, so if you are looking for the ultimate in image quality it is recommended that you choose a fixed value ND.