IGG is also great against quick aggro/burn that can take a large chunk on turn 2 (Rift Bolt, Lava Spike, Chain Lightning? So I start at 10 life for Ad Nauseam after tapping my City of Brass for mana?). With IGG, you can pretty much ignore that.

Though I guess you can Diminishing Returns too and win from there....but IGG just kills so consistently.