You can leave a fridge outside in the winter unplugged but to protect it the fridge should be covered so the elements don't harm the exterior and cause rust to the fridge.
You can also have a fridge outside plugged in in the water as well.
If leaving on vacation and you have no food in the refrigerator you can unplug it to save electricity.
You should unplug your refrigerator if away for 1 month or longer.
Removing all the food and unplugging the fridge will also save electricity and you will return to a clean fridge.
Wipe down the inside of the fridge with a rag and prop the door open to allow ventilation.
If you are going away for a month or longer, it is always a good idea to unplug your refrigerator to save on your electric bill.
Empty your refrigerator, drain the water tank if you have one, clean the inside of the refrigerator and leave the doors open to avoid any unwanted odors.
A freezer can be left plugged in and should if you have frozen foods as frozen foods can last longer and the electricity saved in that instance is not worth the loss in food.
I always unplug my refrigerator after emptying it and leaving for longer than a month but I leave my deep freezer plugged in.