When I’m on vacation, should I turn my unit off?

Yes, if you are considering the equipment alone. Any malfunction, no matter how minor, can become a total system failure if allowed to struggle through a long period. Realistically, you might consider some other factors including freezing weather and broken pipes, pets, plants, sensitive furnishings. Many people compromise by using settings like 85° in the summer and 60° in the winter during vacations. Trane’s Deluxe Programmable thermostats have a vacation program built in.