So I've been rereading the histories, and wondered what the impact of Sicily in the Persian wars would have been. OTL he was willing to send a contingent of 200 ships and 28,000 troops to support Greece in the war, but withdrew support when he was not offered a command.
I think that had the Greeks acquiesced and given him command of the navy, it would have prompted other borderline states like Corcyra to join the Greek cause. I suspect, given that Eurybiades had command of the navy OTL and still ended up following Themistocles plans, that the same could have been true of Gelo, which means that the Persian defeat at Salamis would still have occure, albeit with more loss on the Persian side.
If that were to happen, the Greeks could have followed up more decisively on the battle of Salamis, crushed the Persian navy and blocked Xerxes from crossing back into Asia.
I know it's a lot of 'what ifs', but I suspect Xerxes entrapment and eventual defeat in Greece could have led to the Anatolian and Egyptian portions of his army (and empire) to desert him and result in an earlier dissolution of the Persian empire.