It controlls how smooth the lights in volumetrics are.
0 is disabled. Over 0 is super diffuse and higher you go the sharper the area becomes again.
If you set the values to low, but not 0 it might help with flickering due to there being no pronounced volumetric lights next to light sources and it’s distributed more evenly.
Can’t test it atm so I hope it isn’t changed recently.
Just speculating, but if your scene is built to scale then reducing the volumetric end distance (default 100m) should result more samples being in the range your scene seems to be in and might help a bit.