Metaphors are best used to explain emotions that we don't know how to put into words. For instance: time is money. We associate money with having value, meaning that we also consider time to be valuable to us. Sea of grief is another one. Grief is a feeling that can range from very extreme to not at all. We know a sea is a vast expanse of water; that informs us that the level of grief runs deep or is very extensive.
Some of the best works of literature and poetry in the past and present times have been filled with metaphors. "Shall I compare thee to a summer's day" is a famous one written by Shakespeare. He's comparing the pleasantness and elegance of the summer season to his opinion of a special woman. "Art washes away from the soul the dust of everyday life" came from Picasso, one of the greatest artists of the late 19th-20th century. To him, art is as meaningful as being able to brush yourself off and start a new day off right when you have problems. Dr. Strange uses a metaphor all the time when he says we have to get rid of burp back education. He tries to drive home the point that there is no reason to learn things if you are just going to burp it right back up and not even be able to use it. Metaphors are everywhere and you have to know how to understand them if you want to comprehend what's going on in the world around you.