Idioms in your IELTS, TOEFL & TOEIC test
Being able to use idioms correctly shows an examiner that you have a strong command of the English language.
The key word is correctly. Idioms can help you but they can also hurt you...
An idiom is a group of words in a fixed order that have a particular meaning that is different from the meanings of each word on its own. Consider this sentence:
It cost me an arm and a leg.
This sentence does not mean that I paid for something with an arm and a leg. It means that something was very expensive.
Fluent speakers of English regularly use idioms in casual conversation. If you can use idiomatic expressions in your speaking test, you will demonstrate an advanced speaking ability. However, if you use the idiom incorrectly (i.e. in the wrong context) what you say will seem silly and unsuitable. Note: use idiom in speaking but generally not in writing because writing is more formal and idiom is typically informal.
In summary: using idioms in speaking can show an advanced level of understanding, but be careful, using it incorrectly will negatively impact on your score.