There has been a few clients in the past few weeks were their furnace stopped working and the home was left vacant for a few days which meant frozen pipes and not so nice outcome. But those are the obvious ones. The less obvious is your furnace switch in your home. Some times it is accidentally turned off due to someone flicking switches to see what light it turns on (not realizing its the furnace switch) only to leave it in the off position. This then shuts your furnace down and again if the home is left vacant you could end up with a frozen home.
I would guess that in a year only 1% of the homes I show have some kind of sticker or color to indicate the switch is for the furnace. I would recommend placing a sticker saying 'Furnace' on that switch. It only take a minute to do and could save your thousands of dollars in repairs due to frozen pipes.
Here is a picture of my furnace switch at home:
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