What is the blend option in the layer weight node? What is purpose of the blend option in the layer weight node?
The documentation just says it "blends" between the first and second shader.
It blends the output between all 0 and all 1. This can be most easily observed by plugging the output into an emission shader:



When used as the mix factor for a mix shader node, it will blend between all of one material or all of the other.