Sacrificing things to Greyfax is just one option, you could throw them to Commissar Serverina Raine instead for life and cards, or to The Golden Throne for mana
If you sequence him right, you could have a big turn with Planeswalkers
This effect is very powerful on a commander because of the deckbuilding possibilities and the ability to mess with opponents trying to benefit from those triggers
Perhaps it's because we've been used to the ludicrous prices of cards in recent Masters, but it's refreshing to see a regular set have regular prices for their cards as well
You can sacrifice a goblin in response to removal, make lots of tokens with cards like Mogg War Marshal, and have a sacrifice outlet with Mayhem Devil to kill opponents
They're not too expensive, and they're a very effective way to learn how to play