When you shoot your blank round to scare the BG how will you handle the potential, momentary flash blindness that could occur if this were a night home invasion? You've sacrificed your night vision (at least for a few seconds) without delivering any defensive hit to the invader. That second shot might not be as fast, accurate or easy as you envision.
"But today you just read that the man was shot dead
By a gun that didn’t make any noise
But it wasn’t the bullet that laid him to rest was
The low spark of high-heeled boys"
~Traffic - Stevie Winwood~