Beg to differ. The only thing an ND filter does is reduce your exposure. It does not affect the contrast at all.
The reason people use them is when they’re shooting video if you’re trying to get to the proper frame rate for a “cinematic“ look which is shutter speed twice your frame rate. I.e. if you’re shooting 30 frames a second you want exposure of 1/60, if you’re shooting 60 frames per second do you want an shutter speed of one 1/120 of a second
It’s not necessary to do so but it makes the flow of the images smoother especially for objects on the foreground like if you’re flying low to the ground. They’ll be a slight blur which makes the video seems smoother.
If you’re using a camera that has a fixed 2.8 aperture The only way to bring your shutter speed down in daylight is with ND or polorizer filters or use shutter speeds like 1/800-1/1250 or higher.
It’s not always necessary with a camera such as I am the
phantom 4 pro or the Mavic two pro.
They have variable aperture‘s but even out of variable aperture of F 11 that would only get you to about 1/250 second at 100 iso and a bright sunny day.
And as we all know the sharpest aperture and those cameras is closer to a 4.5 or 5.0. Beyond that you start getting Defraction and it softens your image.
If I want to shoot video and have it look “cinematic” on a sunny day I will put on an ND8 filter and That allows me to shoot 100 iso, 1/120 second for 60FPS or 1/60 sec for 30FPS anywhere between F4. To F5.6
If a bit cloudy, then an ND4.
Again the ND filter only affects your exposure, not contrast. If something is blowing out in the highlights then you are over exposed.