Advantages and Disadvantages of Idiom

Advantages:
1) Idioms are like figures of speech in poetry. They help us to understand. " I was so nervous that I had butterflies in my stomach."
2) Idioms , like poetry, can express a great deal in very few words as in the response to this question. "Are you sure it is okay if we come along with you to that party?" "Sure, the more, the merrier!"
3) Idioms, like poetic devices, can paint a picture for us. "The newcomer was as uncomfortable as a fish out of water."
4) Sometimes the idioms speakers use give clues about their geographic, social, or occupational background.
That salesman is full of more lies than an Irishman is full of blarney.

Disadvantages:
1) Having taught both English and German as second languages, I know what a stumbling block idioms can be. How is the English learner to guess that the literal meaning of "He kicked the bucket?" has nothing to do with the idiomatic meaning of he died? And when the English speaker translates the German idiom literally into "I'll take you around the corner." s/he may think it is someone being friendly to a tourist rather than issuing a death threat.
2) Even native speakers of the same language but of different generations can have communication problems because of idioms. Ask any grandparent how many times s/he has had to rephrase something for a grandchild who misunderstood a sentence containing an idiom in his or her own first language because the idiom was outdated?
3) Peers from different parts of the country may not understand each other because of unfamiliarity with non-local idioms. When my family had just moved from the Chicago are to California in 1960, my sister, upon seeing some hideous outfit, remarked to a group of newly-made girlfriends, "I wouldn't wear that to a dogfight." My sister was quite surprised when the girls burst into laughter and could not stop. They had never heard this idiom, which was so common to her that she did not stop to picture the silly image.
4) Teaching literature becomes more difficult because of idioms because even the teacher may have to guess at the meaning of antiquated idioms if no research is available.