In just his last week in office, Barrack Obama granted executive clemency to 539 American convicts. Many of those pardons were an attempt to ease the consequences of America's harsh sentencing of drug users. However, not all pardons were for that reason:

"In addition to [Chelsea] Manning, Obama in his last week in office commuted the sentence of Oscar Lopez Riviera, a Puerto Rican nationalist linked to several deadly bombings in the 1970s. Among others, he pardoned Ian Schrager, the hotelier who owned Studio 54 and served prison time for tax evasion; former baseball star Wille McCovey, who also got into tax trouble; and General James Cartwright, who lied to the FBI about providing information to journalists." - Quartz Media

A US presidential pardon isn't routine, but it's common enough. It's granted in a wide variety of cases, including serious crimes committed by government officials.