If the temperature inside a house gets below 32 degrees Fahrenheit for an extended period, it’s likely that the water supply pipes and the drain traps will freeze. When water freezes it expands, and if there is no room for expansion it’s possible that the pipe will burst. When the ice thaws the pipe will leak, and in the supply system this leak could occur anywhere. Fixing a burst pipe can be expensive, but the damage from uncontrolled water leakage can easily reach into the thousands of dollars.
A properly-insulated house built to current building codes will probably never experience this problem under normal heated conditions. This means the heating system runs properly, the electricity supply stays on, and the furnace fuel supply never runs out.