Right!
The thing is that there’s no one set of settings that work really quickly and to high quality for every scene ever as every scene is totally different and thus will have different needs in terms of your lighting, materials, motion blur, depth of field and so on.
One of the biggest factors is if you’re rendering with 3d motion blur or 3d dof. Both of these effects are about sampling the “position” or the “geometry” of the object, in the case of motion blur vray is trying to sample the position of an object, just at multiple positions over time. With depth of field, it renders the scene from multiple angles / viewpoints (it’s a bit like the camera is on a path constraint tied to a circle) so it’s doing the same “position” sampling of an object at different angles / locations. Both of these position / geometry type of sampling factors are both sorted out by your max AA sampling. There used to be motion blur and depth of field subdivs controls in vray previous to version 3 but they do the exact same thing as AA controls - fire more geometry / position samples into your scene so it was kind of adding in two more controls that might not have been needed. Bottom line, if you’ve got motion blur or depth of field you’ll need high max AA to smooth it out so you’re looking at a 1 / 50 or 1 / 100 type of situation.
Another situation that you need high AA in is if you’ve got very fine, thin detail. Depending on what industry you work in that could be blades of grass, hair, wire fences or the likes. Again if you’ve got small geometry there’s a chance that when vray is firing AA samples it might miss, so you end up using way more AA rays to make sure your tiny details get detected sufficiently.
For the 2 / 8 example, if you’re NOT using motion blur or depth of field and don’t have really fine detail in your scene then the big factor might be lights and materials. If you’re using really big soft area lights, they tend to get a little bit grainy at the soft edge of the shadows. This is an issue with light sampling - it’s almost a little bit like the AA issue with fine detail except rather than geometry / position samples being fired from your camera into the scene, the geometry / position samples are being fired from the direction of your light. If you don’t have enough of those, it might not be able to accurately detect and define the outline of objects that it’s casting shadows with. This’ll mean that the shape of the shadow will look more dotty and random or grain as we see it visually. Likewise if you’ve got a material that has very soft reflections on it, instead of our camera firing geometry rays, or our light firing shadow rays, this time it’s the material firing out reflection rays from the surface of your object into the scene. Same thing as shadows and geometry, vray is firing out samples in semi random directions and taking back a sample of the object that the reflection sees. If there aren’t enough samples as usual, you’ll get a really dotty result since there aren’t enough “hits” to really clearly define the object being reflected. The long and short of it is that if you don’t have enough material samples, you’ll get grainy looking reflections and a bad result. If you’ve got a simple scene with no motion blur, and no fine geometry but you’re using complex lighting or materials with loads of glossy stuff, then you can use less AA (geometry / position sampling) and instead up your light or material samples to clean everything up.
Now we get to vray 3!
So in vray 3, and in general, Vlado’s thought (quite rightly) is that human time is more important than machine render time. With the universal settings (1/100 and so on) everything was left to the anti aliasing controls to clean up the entire scene. The main benefit of this is that you don’t have to go around your scene tweaking individual material or light settings, everything is handled in one single location. It isn’t as quick as going in and optimizing your scene manually each time, but if you can get 5 shots on to the render farm in a day using the convenient universal settings, that might be far better than tweaking your scenes and only getting 3 shots on to the farm in a day. If they’re rendering overnight then it might not make that much difference.
I personally at the minute use a mix of settings for doing vfx work and most of it is determined by whether I’m using 3d motion blur or not. If I am, it’s generally about 1/50 and a noise threshold about 0.01 and then material samples will be about default 8. If I’m doing something that doesn’t need 3d blur I’m normally around 1/12 for fine detail and then my material settings for the likes of reflections range between 40 up to 240. This is a guide that works for me but a thing of note is my scenes typically don’t have a lot of lights and they don’t have a lot of materials to manage either, so if I want to go around my scene optimizing renders, it would take a lot less time than someone doing a huge architectural scene with a lot of lights and different materials.
Unfortunately there is no rule for what your scene needs, they’re all unique and beautiful 
- Give Vlado’s approach of using min max of around 1 / 50 or 1 / 100 and then gradually raining the min shading rate (this is only in vray 3 by the way) to clean up your materials and lights. If it works nicely for you, great! It’s a quick approach for most scenes in terms of getting a shot out.
