Why did U4 use roughness/metallic vs Specular/Glossiness?

[anonymous_user_bb0e176f1 (anonymous_user_bb0e176f)]

@;122251

Both CryEngine (the new steam version) and Unity 5 are (will) also use physically based shading, unity3d and the free version of CryEngine use the spec/gloss shading method.

PBR/PBS allows for much more realistic materials to be created, and enables the lighting to use the material properties directly instead of the older slower method.

For more on how it works, and why it was implemented, have a look through :
.unrealengine.com/latest/INT/Engine/Rendering/Materials/PhysicallyBased/index.html

Also, article goes into even greater detail on PBR (not specific to UE4, just talks about the method in general)
Adopting a physically based shading model | Sébastien Lagarde

I understand why they’re using it, but I’m wondering why there are two different methods of creating the shaders now; either spec/gloss and rough/metal. I’m also wondering why two companies are going a different route vs. Unreal.

I use Substance Designer, and creating textures for S/G and R/M are very different.