The defrosters are usually alcohol based and wash the lubricant out of the lock. The lock will freeze easier and the action is not as smooth as it could be. I have seen locks that needed real force to turn the key even in summer time because of that. A bit graphite powder cured this immediately.
The defroster should be a last resort and it should not be confused with prevention.
BTW: I agree that itīs a good thing to have defroster with you just in case you need it.
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If it isnīt broken, it doesnīt have enough features yet.