The only time I could think that polarization would not apply, would be a very cloudy day, with no water.
Polarization on water IMO is very important as it will cut the glare, and you can get glare on cloudy days also.
Issues:
1. Polarization is less effect on wide lenses and the Mavic has a wide lens, so you need to make sure the filter has been placed on the gimbal to give the best effect. You can easily check this by just holding the filter and looking through it, and rotate it.
2. Polarization will also tend to create a lighter to darker effect on pure blue skies again mainly due to the wide lens, as it's very hard to completely polarize the entire scene the same. You may also see this as you pan across a scene. As you pan, across the sky, you will also see the polarization increase and decrease.
3. Polarization will work best with the sun at your back or 90 degrees away. As you move towards the sun, the effect will not be as strong.
4. Any Polarizer add a bit of light reduction, but all the Polar pro filters I know of include the PL and ND. Be aware of the light you are working in.
5. Polarization also has a huge effect tree leaves, anything green and fall colors. Bright light on tree leaves IMO really cuts down on the colors and adding the PL, will make a huge difference, allowing more of the natural colors to come out.
I use the Polar Pro cinema series, the 3 that are PL and ND. Mainly use just the PLND4, as I am more interested in stills over video. The larger number filters will help however on video as you are attempting to hold the shutter speed to 120/Fps to 60/fps depending on your video settings.
NOTE, if you use these, make sure you have adjusted the noise reduction way down. For some reason on the Mavic, PP, at least on mine, there is more noise reduction added thus plastic looking blurring. I personally HATE this, and really wish DJI would allow video without any noise reduction. However you can change the settings to under the custom styles. Once you add the filter, play around with all three settings as you can make changes and see the effect on screen.
Paul Caldwell