Swarm Training is when a group of trainers leads a training like a swarm of bees, buzzing in and out, taking turns and training different sections. The reason swarm training is so valuable is it raises up more trainers by giving them hands on experience, sometimes before they are ready, but always with help as they need it.
Or said in another way: If I'm the only one that can train on a certain tool or skill, the spread of the training is limited to my calendar. But if I can swarm train others to train the same tools, that training has a chance to spread beyond myself and multiply. (For a 3 minute video explanation of swarm training, check out this link.)
Raising up swarm trainers helps them grow in their confidence to share the Gospel. At one training I had a college student help me train the 3 Circles. He sent me this text later that day: "Just got home and had a chance to tell my somewhat nominal Christian neighbor about the training, and explained the 3 circles. Hopefully it leads to some follow-up opportunities. It's an awesome mission! God is clearly rewarding your efforts!"