Discuss the nature and scope of these defenses and privileges

discuss the nature and scope of these defenses and privileges:

What is the effect of successfully asserting a defense or privilege to a battery or a trespass:

How far do the defenses and privileges go? That is, is the tortfeasor completely exonerated from any and all liability for the tort, or are there limitations?

And, what legal or social policies are served by allowing a tortfeasor to assert a defense or privilege?

text book is Abraham, Kenneth S. The Forms and Functions of Tort Law. New York, N.Y., Thomson Reuters/Foundation Press, 2017 (Sec. B, pp. 39-40 on Self-Defense and Defense of Others; Sec. B, pp. 41-50 on Defenses: Especially the Privilege of “Necessity” and additional subject matter) address defenses or privileges to imposition of liability for intentional torts against personal or property interests.