2-Pass Transparency is very common in avatar shaders, since you often need to have something like semi-transparent hair together with outlines and other things.
Non-convex meshes are ill-suited for regular transparency as they will encounter sorting issues. Adding a separate pass that renders backfaces only allows you to separate the two and create a stable mesh that can act both as a transparent and an opaque object without issue
2-Pass Transparency is very common in avatar shaders, since you often need to have something like semi-transparent hair together with outlines and other things.
Non-convex meshes are ill-suited for regular transparency as they will encounter sorting issues. Adding a separate pass that renders backfaces only allows you to separate the two and create a stable mesh that can act both as a transparent and an opaque object without issue