Never used the Jungle Swarms, but when I played Tomb Kings, I gathered some experience with Tomb Swarms, which are very similar. Choosing the target is key. I loved doubling up on my friend's Ogre cannon and forcing him to choose between shooting one of the two units about to charge (swarms or Tomb Scorpions), or try to get one last meaningful shot. Though Tomb Swarms have the Entombed Beneath the Sands rule, which makes this tactic easier. Another use was to keep them back and protect the Casket of Souls or the catapults. I guess you could keep them back together with a Bastiladon or Stegadon (which should be charging in, though). I really like the fun little rule that gives other units poison. Too bad they are still rather underwhelming...