When doing video, however, shutter speed is an essential ingredient in the final product. A faster shutter speed results in crisper, more video-like results, whereas a slower shutter speed creates some motion blur on each frame, resulting in a more cinematic result.
In video, the rule of thumb is your shutter speed should be 2x the FPS you’re shooting at in order to achieve a cinematic result. Thus, if you’re shooting 30 frames per second, your shutter speed should be fixed at 60.
The Phantom 3 camera is a fixed 2.8 aperture lens, which means that you have to do something to reduce the amount of light entering the lens if you don’t want to over expose your video. You have two options: faster shutter speed, or a filter.
ND filters allow you to keep your shutter speed slower, while limiting the amount of light entering the lens, so you can achieve good exposure without having to speed up your shutter.