To me, the biggest "event" of the conference in Teheran was Stalin's promise to jon the war against Japan after the war in Europe was over.  The Americans, especially, thought this was a good idea but it turned out not to be.

Late in the war, Stalin kept this promise.  In my opinion, when he did that he helped make the US hurry to get the war over with.  The US did not really want the Soviets to take more territory in Asia because they did not want the Soviets to have more power after the war (looking towards the Cold War).  This may have played a role in the dropping of the atomic bombs -- the need to end the war quickly may have helped lead to this.