Another interesting effect that I hadn’t considered - and could actually be used to replicate in cycles - the type of specular highlights you get in BI (which I know people have been asking for on other threads).
Rather than have the roughness of the negative RGB node smaller than the positive RGB node (which gives a halo type effect) - invert the roughness values - and you force the highlight to fall off quicker than it otherwise would. Examples:
This is a single glossy shader with roughness of 0.4 - lit with two mesh lights
Same scene - but mixing a negative RGB glossy node with a roughness of 0.5. You get the specular highlights from the lights - but little else.
Mixed into a suitable material - you get BI looking specular highlights in a cycles material.
