This something I found online.
As much of Tennessee remained loyal to the federal government and federal forces occupied Tennessee from early in the war, many Tennesseans signed oaths of amnesty before the end of the war. The growing number of Federal loyalists made it easier for Tennessee to rebuild its governmental infrastructure long before other Southern states were able to do so.
I think there would be two motives for signing this oath. 1) To proclaim loyalty to the Union (whether sincere or not) and stay on the winning side after the War; 2) To hide the fact that the signee was affiliated with partisans because civilians who were suspected of aiding partisans were often treated harshly ( e.g. banished to Alabama or some s**t hole north of the Ohio River).
Does anyone have a better understanding?