in detective stories: The police are barking up the wrong tree as usual (i.e. they suspect somebody who has nothing to do with the crime).
The ambiguousness of these interesting word groups may lead to an amusing misunderstanding, especially for children who are apt to accept words at their face value.
Little Johnnie (crying): Mummy, mummy, my auntie Jane is dead.
Mother: Nonsense, child! She phoned me exactly five minutes ago.
Johnnie: But I heard Mrs. Brown say that her neighbours cut her dead.
(To cut somebody dead means "to rudely ignore somebody; to pretend not to know or recognise him".)
Puns are frequently based on the ambiguousness of idioms:
"Isn't our Kate a marvel! I wish you could have seen her at the Harrisons' party yesterday. If I'd collected the bricks she dropped all over the place, I could build a villa."
(To drop a brick means "to say unintentionally a quite indiscreet or tactless thing that shocks and offends people".)
So, together with synonymy and antonymy, phraseology represents expressive resources of vocabulary-
V. H. Collins writes in his Book of English Idioms: "In standard spoken and written English today idiom is an established and essential element that, used with care, ornaments and enriches the language." 
Used with care is an important warning because speech overloaded with idioms loses its freshness and originality. Idioms, after all, are ready-made speech units, and their continual repetition sometimes wears them out: they lose their colours and become trite clichés. Such idioms can hardly be said to "ornament" or "enrich the language".