Ok kinda new back into game haven't even tried to get back into taming yet but i have a question , I have 2 nightmares and 2 unicorns in stable from long ago . All of them only require 2 slots to control currently , and from what i have been reading most now take 3 . But i have failed to grasp the importance of this as from what i gather as they train they will require more slots to control . With that said what is the big deal about the old or legacy ones mentioned?