I don’t know, maybe I missed a few months of the blender community news cycle, but it seems like kind of a difficult-to-work-with concept. Is its value in the fact that it can be more realistic?
They are just compact shaders, with well balanced reflectance, absorbtion, transmission, etc. Basically, they are a middle ground for creating good shaders, fast and easy (at least for most common materials), between creating everything with the basic properties, and specific material configurations.
They should also remove the guesswork in setting up materials “correctly” and doing newbie mistakes. 90% of the stuff I do is basic diffuse and glossy with fresnel (sometimes I drop the glossy knowing realism will be sacrificed) so I’m setting up that manually every time. The rest of them are too complex to be handled by ubershaders due chains of interconnected groups. They may be a good starting point for people who don’t want to spend time learning it, as they’re typically designed to “not get it wrong”.
I went away from using my own “PBR/Uber-shader” thingy because it relied on a rather heavy library of math functions that I preferred to link in rather than append, but it proved problematic taking workfiles between locations (missing files, paths etc).
But as Secrop says, the main purpose is ease of use where you don’t have to think, just plugin the stuff you need into respective sockets.