I would say that if you are defending yourself, then you need to be in a defensive mode.
If you are not actually defending yourself, then you could face legal issues.
If someone is in your house, and you don't know where he is, let the law enforcement people clear him out, because if you go after him, you are not in a defensive mode anymore.
As far as defending yourself with a long-gun in a house, just make sure that it isn't so long that it could possibly "clothesline" you in a doorway.
In other words, be sure that it is shorter than the narrowest doorway that you might be going through.
The bottom line is: Defend yourself, your family and your property with whatever you need to, or have available.