Quote from stevegee58:
There *is* that possibility of the unlikely event that one day the market gaps down (or up) through both strikes of your spread. In such a scenario, you may not have had the chance to get out at a 20% stop loss leading up to the gap move. This would most likely happen just when you said, during a period of increased volatility after you've put on spreads during lower volatility. In that case you'd be uncomfortably close to a potential gap move.
In a big gap move, it's truly disastrous.