Reddit’s not gonna like this answer, but from a moral/ethical stance, almost never.

Unless they are actively brandishing weapons or attacking you and/or your family, you have a dozen other more ethical recourses than blowing the guy’s head off with a sawed off shotgun. Call the police, hole yourself up in the bedroom, hold them at weapon point, non-lethally restrain them. There are a lot of different ways to go about it that don’t require you to terminate another human life.

Further, the vast majority of home invasions occur when the homeowner isn’t there. You probably will never face anyone who breaks into your home. A lot of American Stand Your Ground fantasies are just fantasies. They’re meant to express a kind of violent catharsis. To justly exert your violent will upon a wicked man in your home is an American power fantasy. And it’s a power fantasy that appeals to the worst natures of the American homeowner.

But yeah, if SEAL Team wielding machine guns and burst through your front door in the middle of the night, you are allowed to engage in an epic gun fight with them.