Think about the creatures you can afford to reanimate (or hard cast) when designing your deck (and mana base), and also the additional utility of cards like Eureka, and how they could potentially interact with large creatures stuck in hand
However, if you can find a way to discard Emrakul for cheap, you can reduce Emrakuls casting cost significantly
Affinity decks love Inkmoth Nexus as well, and it's occasionally used as a win condition in some combo decks
For example, an X mana symbol does not usually add anything to a cards mana value, except in specific situations
Thanks to this, you can play all the best creatures and spells with Proliferate, alongside classic Infect cards
The ability to turn into any kind of animal has to be somewhat useful