Shader code is extremely performance sensitive, and poorly written or complex shaders can absolutely destroy framerate.
Conditionals, loops, and even function calls on bad drivers are all things that need to be avoided, when possible, and it's very rare you can get ship a game without having to spend time optimizing your shaders.
Conditionals, loops, and even function calls on bad drivers are all things that need to be avoided, when possible, and it's very rare you can get ship a game without having to spend time optimizing your shaders.