Besides keeping them from being knocked away by melee?
JP does not prevent fireball from being knock back.
Hangman Knot is the skill that root all the link object. (Root prevent knock back.) however HK only last for a few second. 2-3sec? i don’t remember LOL
You can link them with the monsters and pull everything together which will cause them to take the ball’s damage (no pun intended), besides, when the balls take a hit (again, no pun intended) the monsters will be hurt.
It also makes it possible to debuff a boss when there are no enemies around for that extra lightning damage.