It's covered pretty well in depth here: http://politics.stackexchange.com/questions/7674/why-is-the-us-president-allowed-to-grant-a-pardon http://politics.stac

It's covered pretty well in depth here: http://politics.stackexchange.com/questions/7674/why-is-the-us-president-allowed-to-grant-a-pardon http://politics.stackexchange.com/questions/7674/why-is-the-... Some of the finer points: - A presidential pardon is for federal crimes. The president cannot pardon someone for a state crime (or a crime committed subject to a local jurisdiction whose power is derived from a state). - Presidential pardons are reinforced by the constitutional prohibitions against double jeopardy and ex post facto laws. Once a person has been pardoned for a federal crime, the federal government (and any territories or districts that derive their power from the federal government) cannot re-try the pardonee for that crime. As pointed by another person in the same thread which really answers your question: - Fourth major benefit of pardons: Presidential pardons are about checks and balances. The legislative system has determined a law, the judicial system has determined an infraction of that law, and with a pardon the presidential system can react to a mistake made by either the legislative or judicial branch.