I think the point is not so much the law but what is better for the fish. People can get great pictures of fish while they are still in the water so why not do the right thing and keep the fish in the water. Also understanding the law may help in a tournament situation.
Something that others may not know is that if the gaff clears the gunnel and the fish is lost it should not be counted as a release but rather a lost fish. The intent was to kill the fish but was lost in the battle.