A more computer-like metaphor for Dead vs. Poetic Metaphor.
Examples of dead metaphors show quick understanding of a speaker or writer's meaning. I observed that it often takes more words to describe a dead metaphor's literal meaning than the dead metaphor itself.
More words – especially a sequence of words that aren't rote, like a dead metaphor's sequence of words is – would seem to require more calculation to "unpack" the meaning than just doing a quick cache 
lookup. Think of dead metaphors as being like something like the key into a hash table . With that key, you can quickly look up the meaning.
A poetic or Generative Metaphor is about deriving *new* meaning, not looking up a rote or stored meaning. That's novel calculation.
So my theory is that all metaphors are originally poetic: they require thinking even for understanding. A frequently used poetic metaphor becomes dead when it stops prompting calculation and is only used for lookup.
For more, see Learning Balls to the Wall.