A catastrophic stop is not the trade's exit. It sits well outside the working level - often two to three times the intended stop-distance - and exists purely so that an unattended account cannot be destroyed by one event.
Think of it as insurance with a deductible. On a 1% risk trade, a disaster stop at 3x the normal distance caps the accident at 3% instead of whatever the market feels like. That is the difference between a bad week and a rebuild.
It matters most for mental-stop traders, overnight holders, and anyone trading from a laptop on hotel wifi. It does not protect against gap-risk - nothing resting in the book does - but it does protect against outages, freezes, distraction and the specific human failure of watching a position fall while deciding what to do.
Related: mental-stop, hard-stop, gap-risk, worst-case-loss