Can nodes and OSL be used to create the same materials, or is there something you can do with OSL that isnt possible with only nodes?
Nodes give you a lot of possibilities, but you can’t do everything with nodes only.
Check out this blog for example, you can’t do most of them with Nodes only. http://blenderthings.blogspot.co.uk/
In OSL you can create new, unique textures, and you iterate over data (“for” loops as an example) and that’s not possible with Nodes.