But do they actually work? I don't know about Nixon, but I'd argue "draft dodgers" weren't guilty of any crime at all. Perhaps Uncle Sam was scared of that being proven in court as a precedent for future wars? With Trump's pardoning of Arpaio after conviction, that actually means something, because to be convicted is to be legally guilty, so I wouldn't put that one in the same bucket.
During Vietnam, nearly every male 18-26 was required to register for the draft. Failure to do so was a felony. At lot of Vietnam draft dodgers simply left the country. Some were charged with crimes; but many weren't, they got away completely undetected. Carter's pardon was a blanket pardon for all those who had been charged and those who hadn't.
Trump's pardon of Arpaio
was a bit different, but it was still outside the bounds of the conventional. His pardon included the phrase "any other offenses that might be charged." He gave Arpaio a free pass for any charges with which he had not yet been charged. This is essentially what Biden's pardon said too: "including
but not limited to all offenses charged or prosecuted."
If this is something that interests you, you should check it out; it's all public information.