James Clapper, the Director of National Intelligence, lied to Congress in March 2013 when he said that the NSA was not collecting data on millions of Americans. He told this bold lie despite the fact that he had been provided the question in advance by Congress.
See http://www.theguardian.com/world/2014/jan/04/clapper-lie-congress-nsa-na...
I don't expect Mr. Clapper to ever be prosecuted. However, if the President pardons him, it at least makes the point that what Mr. Clapper did was wrong.
I think that is a pretty important point to make...