trying to understand global subdiv parameter

[Morbid Angel]

from vray help:

Global subdivs multiplier - this will multiply all subdivs values everywhere during rendering; you can use this to quickly increase/decrease sampling quality everywhere. This affects everything, except for the lightmap, photon map, caustics and aa subdivs. Everything else (dof, moblur, irradiance map, brute-force GI, area lights, area shadows, glossy reflections/refractions) is affected by this parameter.

I am curious as to how this works exactly. Lets say I have a scene where there is a single vray area light with 8 area samples. With global subdivs multiplier at 1 it will get 8 samples. With global subdivs samples at 16 it will get 8x16=128?
if so, then wouldn't the render time be the same if you were to set 128 samples in area light when you have global subdivs at 1?

[zoranm]

That is my understanding as well. It's a covenient and fast way to increase globally stuff that has some sort of subdivision parrameter.
I burned myself couple of times with DOF and global multiplier accidentaly left on 8!

zoran

[duke2]

It's a good way to do quick tweak renders as well. Just whack it down to 0.5 and you'll get quicker renders while doing material/other stuff.

[muoto]

I usually leave all the settings at default, and set the global subdiv at 0.25
Renders much faster and i do not see any (big) difference in quality when rendering at big resolutions (3000px wide or something)

[Morbid Angel]

im curious what vlado has to say about this?