What does make a long story short mean?

Where does this phrase come from?

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According to Cambridge Dictionary used when you do not tell all of the details. 

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https://dictionary.cambridge.org/us/dictionary/english/long-story-short

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When do we tell stories like this? Why do we use them? Who do we usually tell these types of stories to? Why are they useful? 

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Example: To make the long story short, I got fired.

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When and why would this story long story be appropriate to tell?