It's used like any other self-justifying memoir. It's a primary source record of Jefferson Davis' opinions during the fight against Reconstruction and for the conduct of the Confederate government during the war. It's historiographically important as one of the key texts in the bedrock of Lost Cause mythology. It also gives exhaustive detail on the actions of his administration. For those reasons, I've seen it quoted by McPherson, Foote, Levine, and many others.