I use it at the start of the fight, and then whenever the group is gathered together.

Such as on fights like Alexander 4, I put Eos/Selene in the middle of the room, and Deployment Tactics on her. So the spread hits everyone even though I'm far from those groups of people.

Using Deployment Tactics on your fairy when shes close to melee/tanks is an awesome way to get that cover in without needing to run in and succor o/