I can't seem to find any decent guides on this game.
The obvious benefit of the skill training is the increase in skill cap. I've read from guides on the internet that the Alchemist reduces potion costs. The workshop reduces cost of enchantments. The necromancer does I don't know what. nothing from what I can tell.
The dialogue in the Necromancer platform and the Workshop said they would create the ultimate demon and make the ultimate weapon. Yet they didn't do either. =(