Making Long Stories Short

What does make a long story short mean?

Where does this phrase come from?

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

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? 

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

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

Long Story Short IMage 1 - August 16 202

How do you make a long story short and effecient? What important plot points do we choose to help get our story's point across?