- A disaster is heading your way that will kill you (wild fire, flowing lava, Cat 5 hurricane, massive flooding). You can't bug in if the disaster heading your way will wipe out your home.
- You or a loved one has serious medical issues that could kill them without proper medical care. If a disaster is heading your way that will likely wipe out medical services/EMS services in your area, bugging out to a safer location is the best choice to make.
- If the disaster may close the only evacuation route from your home (unless you have a helicopter/private plane and can self-evacuate at the last minute if needed).
- If the place you live is under a mandatory evacuation order. Once a mandatory evacuation order is given, those who choose not to evacuate will not be able to call 911 for rescue (first responders aren't going to risk life and limb for people who chose not to evacuate when they were told to).
- Your immediate area becomes unsafe. This is usually a short-term bug out and happens when a situation such as a train derailment or the like makes you fear for your health or safety. A year or so ago SWAT blocked off our entire neighborhood and it looked like they were planning on a full-fledged shoot-out with our barricaded neighbors. The spouse and I decided to leave for a while, catch lunch and a movie, came back and saw that the neighborhood was still blocked off so went shopping, and ended up spending about ten hours away from home. It was a safer choice than waiting for the bullets to start flying.
- A CBRN event happens and is spreading in your area yet you still have time to leave. Chemical, biological, radiological, and nuclear events often necessitate leaving your home for a safer location. Even if you have PPEs and your home resembles a BSL 4 lab, often putting distance between you and the threat is the best option.
- Your country is going to Hell in a hand basket a la Venezuela or the Nazi era in Poland/Germany in the early 1940s. Massive civil unrest spurred by a tyrannical government means you may have few options for safely "bugging in" no matter how prepared you are for long-term survival.
- The area you live in has been poisoned. If, for whatever reason, the air/water/ground has been poisoned, long-term survival in your area may be impossible and thus necessitate bugging out even if you survive the initial problem such as contamination of the ground water from mining activities, a Chernobyl event, etc.
While bugging in is usually the best and most logical option, being prepared to bug out is necessary when it prevents serious illness, injury, or death.