Metaphors redirect exactness. They reduce the friction of being honest and straightforward.
Having “a lot on your plate” is more gentle than saying that you have tons of work to do.
Saying that a person's “a walking dictionary” is to say that they're good with words.
“America is a melting pot” means Americans come from diverse backgrounds.
Metaphors help illustrate the truth without having to say it like it is. Metaphors are soft and illustrative.
It's much faster to impress an idea when we can fabricate an image in mind.
We remember 2/5 of what we hear and 3/5 what we see. Together, metaphors help us communicate 100%.