it's a disadvantage, and a big one at that
Unlike firebending cards, you retain the mana so you can throw a Yargle under the bus to get out a Crackle with Power, or you can pour mana into Ozai's activated ability, which interacts with cast-from-exile synergies
Each pack contains a combination of 14 Rares or Mythic Rares, 710 Uncommons and Commons (maximum of 7 may be Uncommon), and 1 Land card
For Affinity, it was equipment, highlighted by Skullclamp and Cranial Plating (which wasn't itself banned but certainly helped create the insane Affinity decks that led to mass bannings)
I would be remiss if I mentioned this without also mentioning my favorite aura
From Burnished Hart to Oblivion Stone to Nevinyrral's Disk to Skullclamp and all equipment to Sensei's Divining Top there are tons of ways to build around and abuse this