Well, of course the other person needs to understand us, of course. :) Also, when we use an idiom, we are creating an image which describes the situation. Basically an "as-if" situation. When do you choose to use idioms in Indonesian?

Idioms are usually used in less formal conversation. It is best to avoid them in formal writing. It is also advisable not to use them too frequently. Some idioms also are more familiar to people of a certain age, geographic region, or culture. When in doubt, it is best not to use an idiom. As you hear more native speakers and read more, you will begin to see when it is appropriate to use idioms.

English is so filled with idiomatic expressions that it is difficult to avoid them.