NEVER NEVER NEVER shoot at anything you cannot see.
The guy that was screaming at your front door might have just become the police man banging on the door to see if the guy his partner is chasing down the hall right now just killed someone in your apartment.
NEVER NEVER NEVER shoot at anything you cannot see.
While this is likely true in 99.9% of circumstances, there are a very few instances in which shooting at something you cannot see could be a legitimate course of action.
Situation 1: you have positively identified that an intruder is in your home and have retreated to a "safe room". You are absolutely certain that the intruder is still present in your home and he is not just banging on the door, but actively attempting to break it down. In this circumstance, I could see shooting your attacker through the door.
Situation 2: you are being actively attacked in darkness. Your attacker is at contact distance but, due to the lighting, you cannot see him. In this situation, shooting your attacker, even though you cannot see him, would be a legitimate, and quite possibly only, viable course of action.
Situation 3: you are accosted while seated in your vehicle and, for whatever reason (heavy traffic, disabled vehicle) you are unable to flee. While you can see and clearly identify your attacker, you are forced, due to the way you are positioned, to shoot through part of your vehicle at a part of your attackers body which you cannot clearly see. Like situation 2, shooting at something (or at least part of something) that you cannot see may be your only viable option.