If Cheney is lying now, he is lying about whether or not any important or useful information was obtained thru the use of water-boarding. No such information has been released to the public, so we don't know the answer to that question.
We did not use water-boarding in World War II, or in any of our other wars, yet we always managed to obtain the information we needed from enemy POW's, using other methods.
Several key CIA agents have testified recently that there are much better ways than coercion to obtain vital information from enemy combatants. Creating a rapport between the CIA interrogator and the prisoner works much better than the use of coercion in obtaining reliable information.
So, Obama contends that, even if Cheney can ultimately show that water-boarding did in fact produce some useful information, the same information, even more complete and reliable, could have been obtained by using less coercive methods.
Using water-boarding and other coercive methods hurts us by giving the enemy a propaganda and recruiting tool, which Al Quaida has been using effectively. If we don't need to use these methods to obtain reliable information, then why hand the enemy the gift of an anti-American propaganda tool to use against us?