At close range, i.e. across the room, a too-heavy shotgun or too-heavy rifle can be "shot from the hip", much like sinking a cue-ball into a corner pocket. That will save your shoulder, and will make follow-up shots much easier.
A corner pocket is about 4.5 inches. The center mass kill zone on a man-size target is at least a 10" or 12" dinner-plate wide. Even if you miss the heart/lungs, getting gut-shot with 12-guage buck-shot or slug might not kill immediately, but I suspect the attacker's priorities will shift substantially.
If someone got in that room, he would be hit with buckshot in the face followed by 38 special hollow points in the chest. (My specialty is chests.) I'm real serious when I shoot.
I can wad up a piece of paper and hit the inside a trash can across the room. Yes, I played basketball and coached a girl's high school team. Keeping your eyes on the target is what makes that paper/basketball go in. It's the same with bullets - keep the eyes on the target, don't waver and the bullet will go where the eyes are aimed. It works for me whenever there is a target and something needs to hit it.