Do you mean like, Giants and other monsters, or things like Skirmishers or Salamanders?
I think that - in a min-maxed army - folks wouldn't really use them at all. I think they're characterful, more than anything else.
In 7 times 7 aeons when I have gotten around to my Tomb Kings, I will use the Giant and a Scorpion model simply because I have them and want to say I have an army with at least 1 of everything!