Ok, people.
Lets imagine 3 different dataset. 1st from Nikon D810, 2nd from Canon PowerShot G7 X and 3rd from Samsung Galaxy S7.
All have datasets have camera in same positions. And the same image resolution, lets say 12Mpx.
How work modes in RC:
Draft - 3~4x times downscale images, minimal mesh optimization.
Normal - 1~2x times downscale images, mesh optimization and refinement.
High - No image downscale, maximum mesh optimization and refinement.
So on default settings, there is no question about Draft/Normal/High, Draft use 3-4 times smaller images for Depth maps, Normal - 2x smaller, High - Full resolution.
All datasets except Samsung one will have more details and as result bigger mesh count in High comparing to Normal. Samsung probably near the same 
If you change default settings to Normal and disable downscale. There will be a different result.
Probably only Nikon D810 dataset will have much more details in High due to sharp images and no AA filter. And more mesh calculation steps comparing to Normal mode.
G7 X Probably will have the same amount of details and probably a bit bigger pol size. Actual details will lost due to lower amount of details (AA filter, ISO noise, etc, chipper camera).
Samsung dataset in High mode just will have increased number of poly without any real details.
So if you have sharp, clean dataset with good overlap, good textures, low reprojection error after triangulation etc. And if you need maximum possible details, you can use High.
If you use middle class camera, often making errors in overlap, dof, etc. Normal with disabled downscale is enough.
If you use smartphone camera, than you should not use High because it not give you more details.