Note that it's talking about cross compiling from HLSL to GLSL, and it's also talking about mobile devices. If you're writing the GLSL, this shouldn't be necessary. Keep in mind that the article states that "mobile platform drivers are quite bad at optimizing GLSL." I'd guess that PC drivers are good at such optimization. High level shader languages like HLSL, GLSL, and Cg are designed to be automatically optimized at runtime by the video card.