Have you ever heard someone say something like the following?
I was so scared that I literally jumped out of my skin.
I was so cold after two hours in the snow that I literally froze to death.
Upon hearing a statement like one of these, I think, “Really? You literally jumped out of your skin?” Or, “You actually froze to death, but you’re still alive to talk about it?”
It’s common to hear figures of speech (like idioms or hyperboles) used for emphasis, just as “jumped out of my skin” is used to express extreme fright. Such expressions are not intended to be interpreted as is, which is why they are considered figurative. In contrast, when something is literal, it is real or actual. Obviously, it is impossible to jump out of one’s skin, so this expression is figurative, not literal. The use of literally in such an expression is incorrect or, at best, unnecessary.
It could be argued that literally is used with figures of speech for the purpose of exaggeration or emphasis; that is, the person including literally is doing so purposefully to extend the hyperbole. But it is generally understood that figures of speech (as used in the examples above) are for emphasis, often involve some exaggeration, and not intended to be taken seriously. To include the word literally for further exaggeration or emphasis is, in my opinion, verbal overkill.