As per title - I assumed that this could be handled by the IOR in the vray material.
my understanding is, it’s a viewing angle thing.
It is but don’t you get the same result by ticking the Fresnel box in the vray material?
I think with IOR you can’t easily control the amount of front on reflection vs the side reflection amount.
I think some people just like to play around with the curve.
Via Falloffmap you can control the specific behavior of reflectivity and glossiness not only by custom curves but also by textures.
Gives you much more control.
because typically the boss or the client says to make the glass more reflective. Then in the falloff you just make the black swatch less black. It’s easier to “cheat things”
if you only have fresnel ticked and reflectiveness is 255,255,255, it will be more “accurate” but often then you loose reflectiveness on glass when viewed perpendicular. Then just cheat it with falloff map set to fresnel and make the black something like 20,20,20 for example depending on your needs
Ok that clarifies things - thanks 
I never find myself needing to use a falloff map to control/create Fresnel reflections. Simply by ticking Fresnel reflections in the VRay shader I can create any kind of material I need, with any kind of reflectance values I need. What a lot of people neglect to mention is that the IOR controls reflectance when Fresnel reflections is ticked, meaning you get more metallic reflections (perpendicular to viewing angle) as you increase the IOR, and more plastic/rubber style reflections as you decrease it.
Yes the IOR Fresnel option is more realistic and physically accurate. However if you want to increase reflection on faces facing the camera u can not do it. There for you have to use Falloff map. Its for artistic purpose and in some cases for more advance users to take the advantage off.
…Yes you can, using the IOR.
The IOR changes the direction of the reflection. With falloff map you can keep the direction the same but increase the reflection
No it doesn’t it, changes the direction of the refraction, not reflection. The reflection angle stays the same regardless of IOR.
We more often than not tick fresnel on in the material and control the falloff using the IOR, but this is quite arbitrary (to me as an artist, rather than a scientist).
Sometimes, if I predict that we are going to want to fake things (i.e. have strong reflections when looking directly perpendicular to the glass/metal/reflective surface, but also have strong - but not as strong - reflections at glancing angles), I will use a falloff in there instead.
No you cant. If you want to increase reflection of faces facing the camera and don’t change reflection of faces facing away from camera you can not do it using IOR. Fresnel increase it all not just one or another angle.
This thread is making me think of “Rush Hour” where Chris Tucker tells Jackie Chan: “My daddy will kick your daddy’s ass”
Hahaha. Yes!
This is why I ‘usually’ write things like “I think” or “in my opinion” in case I am wrong (and I usually am!!!). So, in the film Rush Hour, I would say something like:-
“I think my daddy will kick your daddy’s ass” or “My daddy will kick your daddy’s ass, in my opinion”!
So people would tend to use one or the other and not both in conjunction?
Just asking for general learning.
I thought that direction of reflection was based of of surface normal not from IOR?
Direction of reflection is based on surface normal UNLESS there is bump/normal/displacement.
IOR only control the strength of the reflection.