I cant remember from the top of my head - because i have barely had time to use the exporter, but IF i remember correctly the Optimized one is for more stylized/cartoon like stuff. I will double check and get back to you!
Just export it and look at the outputs ;) The optimized version packs greyscale channels together and uses fresnel from diffuse using metalness (also packed in a channel) as the mask. It's the same data, just using less texture lookups, if you don't understand how it all works, just use the regular way (bit more of a…