If you have a lawn mower and it's sitting in your driveway and someone walk's up and takes it and you shoot them your going to jail and in trouble because it was theft and not burglary.
Same lawn mower and it's in your garage and the same person walks into the garage and takes the lawn mower it's now burglary and you can shoot him legally.
Same for your car. If they broke into your car and are taking something out of it and you see them with something in their hands like a radio etc. then it's legal to shoot them. If you catch them on the outside with a crowbar then you need to wait till they get inside and grab something then shoot them.
Just kidding. He made a point to stress that although you may be legal it's not worth it. Also, he said that night time put's a whole other twist on it legally in your favor. My instructor was an officer in a large metropolitan city.