"Show me just what Mohammed brought that was new, and there you will find things only evil and inhuman, such as his command to spread by the sword the faith he preached." - Manuel II Palelologus
Castle Doctrine in most places applies to a place you control by ownership, rent, agreement, or employment. Stand Your Ground applies anywhere you go. It’s a minor distinction, but if you get mugged on a city street, Castle Doctrine doesn’t apply because you do not have control over the area. Stand Your Ground changed it so that a person can use deadly force for defense anywhere that they have a legal right to be. Like I said, it’s a minor distinction, but it’s still important because some RTC states also have duty to retreat laws still in place.
In some states, if a mugger pulls a knife, you have a legal duty to attempt to escape before you can use force. In Stand Your Ground states, you can use deadly force as soon as you believe that your are in imminent danger of death or serious bodily harm.
It also makes a difference on private property. New Jersey has a fairly decent Castle Doctrine, but it only applies to, “lands controlled by you.” Suppose you’re friends with your neighbor, Farmer Joe. Farmer Joe gives you permission to walk your dog in his fields. While there, you see your other neighbor, Drunken Trailer - Trash (a hyphenated American) stealing the parts from Farmer Joe’s tractor. You confront him and he threatens you, raising his wrench above his head to make it clear that he will use it as a weapon.
In New Jersey, you are not protected by the Castle Doctrine. You do not control the land. Stand Your Ground protects you from prosecution because you have a legal right to be there, and therefore you can answer his threat with deadly force.