if you gamma correct transmaps or displacement maps or bumpmaps, you alter the values of the maps and therefore their effects on the model. eg, a transmap works on black and white and grey. if you GC it, you alter it's effect on the model from what was intended.eg - an area which was supposed to be masked out, can then only be partially masked. or a displacement (I learnt this one!) can be reversed.

I hope this makes sense (or someone can explain it better)

Airport security is a burden we must all shoulder. Do your part, and please grope yourself in advance.