Synthetic ATF?

I understand the benefits of synthetic fluids. Any motor that I have gotten fresh has had synthetic oil in it. Use synthetic wheel bearing grease & gear oil as well. But ATF I just have a hard time with. Spoke to my buddy that owns a trans shop about it. He would not go any further than saying that from a shop stand point it is just to costly to use. As he puts it he is already getting bent over a barrel purchasing conventional ATF. Could be I just do not understand the workings of a slush box but with ATF being hydraulic fluid, more or less, what is the advantage of synthetic? Perhaps this is where my ignorance comes in, with my thinking that ATF is more or less just hydraulic fluid.....So, can some of your folks please edjewmookate me???