The Downscaling Factor will reduce the resolution of your images by a factor of 2 or 4 (half or quarter). The point use will be adjusted accordingly. You can make this selection in Step 2 of the new DJI specific upload workflow.
Downscaling can help mask the complexity of bare trees or vegetation if you are having trouble processing those areas. The tradeoff is that your GSD will be larger.
If the Downscaling Factor says 'None' that means that there is not one used and the imagery will be processed at native resolution.