You can't be surprised when something you never use is broken when you do go to use it.
Remember too, the defrost will cycle the AC and if the AC unit pulley fails you will toss the belt.
So it's good to know what is going on.
The heat can also alert you to cooling problems, if the heat blows cold, you know there is no coolant in the heater core, which could be a few different issues, none of which are good.
Pretty much nothing mechanical was meant to sit and do nothing and all parts need to be exercised.