I've noticed that this option is more important when taking ground scans with HRM than on normal A-A/A-G scans.
On my 5800x3d (8c/16th), 4k, high textures and extreme distance, with option set to 12thread I noticed "medium" stutters when doing HRM snaps.
RivaTuner overlay was clearly showing some spikes, I changed value to 8 threads and there was slight spike in timeframe but no stuttering anymore. This is only when HRM renders snap of piece map.
With TGP "on", cpu usage is even more. I went down to default value of 4 and all is working fine, I don't have any spikes on frametimes so my conclusion is to leave it at default 4, I saw zero profit in game comfort for changing it higher.