I imagine some use of smoke grenades is involuntary, e.g. when retreating, a man may throw smoke or a vehicle might pop a spread of smoke grenades as a matter of course, and so this action would just be an addition to the standard text for a unit retreat result. Directing smoke at a point, from a tank gun or a grenade launcher (to cover movement or retreat, or to blind a powerful enemy vehicle or heavy weapon) is more of a voluntary activity.
In ARMA I’ve seen medics throw smoke to cover treatment of a fallen soldier, although this is probably something that happens in ARMA more than real life. A medic might do it to allow the casualty to be dragged to hard cover.