A lot depends on your location, we live in the colder north.
I set the thermostat at 10C (about 45F) and the stat is web enabled so I can check on it at any time. If the temp drops below 8C an E-mail is sent to me and the house checker. I shut the water and water heater off. Since most of the water lines are in the basement the temperature there doesn't vary as much as on the main floor. We had a power interruption for over 24 hours last winter due to an ice storm and the basement temp was still above 8C when the power was restored. I would be concerned about house damage if I didn't heat the house given our winter temperatures