What exactly does the threat of sanctions against Iran accomplish?

On a good day a large part of the third world, most Islamic countries, and a couple of super powers would favor Iran in a call for sanctions. With the oil situation being what it is, and with Iran rolling in petro-dollars (petro-euros now?) and oil what is the chance that Iran cant get what it wants sanctions or otherwise? Is all this sabre rattling just to demonstrate that the west did something, regardless of how useful it was, as Iran goes nuclear? If you were the US prez now with four years to go and didn't need to posture for any future election, what would you do? I dont envy W, McCain, or BO - if we had Saddam, we may have been able to get him to keep them in check.