And, bringing Assange to court will introduce all the background evidence he holds.
Further damning HRC and the Clinton Foundation.
Especially the Haitian orphans.
A pardon would eliminate all that from court proceedings.
I’m not sure you would have to prosecute Assange in order to get him to testify about Seth Rich and other Deep State crimes of which he has knowledge. Maybe it would make more sense to do it that way, but he could conceivably be pardoned before hand and still testify as a material witness in individual cases brought against the Clintons, DNC, etc.