I wouldn't necessarily teach them to beginners but I would explain what they are (perhaps giving examples in their own language) and, whenever you stumble across one during something like listening/reading comprehension, I would explain it in full.
In my humble opinion, idioms are important to learn like any other aspects of English. This is because they'r used in very day conversations, media, and so on which make them a matter of necessity than choice. Thank you for reading.