Evacuations are more common than you might realise.
A gas leak might lead the emergency services to evacuate a street. Flooding may require you to leave your house or workplace. Not all evacuations are long term, sometimes you can return after a few hours once the emergency is over.
However, just think about a chemical incident. Your house might not be habitable and you might have to be re-housed while decontamination is carried out. Therefore, it is sensible to prepare for an evacuation.