The only time I would use them (if I carried them) is when the enemy is over running my position and I need to make a get away. The smoke can get you "lost" easily from enemy eyes and allow you to set up in another position, in which you can engage the enemy once again.
Besides that, I can see using them by throwing them at the enemies position when setting up a squad ambush, circling them and firing into the smoke with support gunners, but this is something that takes a lot of team coordination.
Besides that, I can see using them by throwing them at the enemies position when setting up a squad ambush, circling them and firing into the smoke with support gunners, but this is something that takes a lot of team coordination.