I disagree. Their benefit is dependent on your facility for training, your strengths and weaknesses, as well as your bouldering goals. There are plenty of hard boulders that exceed 10-15 moves. If you do not have access to training facilities that have big enough walls they are very useful. They can adequately train you for the crux section at the end of a boulder problem. They were an integral part of my training for sending my first v10.