I got a goal of assigning 30 Dwellers to the right room and was stuck for a moment as my vault is already optimized.
I have a whole floor of nuclear reactors with everyone wearing radiation suits. I found that changing to military fatigues or other +S clothing then dragging them to the next reactor room works, even if they have 10 S.
Dress then drag a room at once and the task is done in a few minutes. This would seem to be a reason to wear sub-optimal outfits.
Hope that is of use maybe.