OK so I did some testing: (all other settings on HIGH/ULTRA. 500mbps internet. No rolling cache. No manual cache.)
Terrain LOD seems to affect the overall draw distance of everything, and more spesifically the ground elevation data, PG quality(range) and possibly bing imagery quailty(?).
Sidenote: Theres buildings up close that changes quality only when you get to 400LOD - which is worrying. You can see the quality-“rings” shift further out as the LOD increases. I worry these have been “tuned” too much a while back (the closest high quality ring is just at that warehouse building to the right at 400! LOD).
Here is where I am a little bit confused. It seems like Objects LOD affects the quality(range) of handmade custom mesh objects in the scene (example the boat and some of the buildings, but not the PG).
Buildings seems to affect the quality/complexity(range) of autogen buildings, and their draw distance.
Trees seems to affect mainly the density and draw distance of trees.
There seems to be no difference what so ever betwen OFF and ULTRA in this portion of the UK.