Utilizing neutral density filters (ND filters) can be a major benefit to do drone photography. By using these filters you are lowering the amount of light to come through your lens. This in turn lets you lower your shutter speed so you can get buttery smooth video clips instead of choppy ones while still maintaining the correct amount of light to come through the camera's sensor.
A Neutral-Density Filter, or ND filter, reduces the amount of light that enters a camera’s lens. Under bright sunlight, an ND filter allows photographers more leeway in selecting an aperture and shutter speed by preventing overexposure.
The Mavic Air 2 fly more combo comes with a ND filter set and includes ND16, ND64, and ND256.
The number associated with an ND filter indicates how much light enters the lens in terms of a fraction.
So what ND filter you should choose depends on the amount of light around your and the effect you want to achieve.