If you are one of these people who uses them during your training, can you stop please. Getting randoms who've never met each other to join together and work on something they have literally just been introduced to and so know nothing about is lazy teaching and utterly, utterly pointless - no-one is sure what they've to discuss, they're don't learn from others who are as clueless as they are, it's bloody awkward, there's so much wasted time as everyone looks blankly at each other, and actually, they're attending the session to learn from the person who knows the subject.
I've just left another session at the breakout rooms point and have decided I won't attend another one ever. It's very liberating!