Within an enclosed greenhouse / grow room, misting can increase humidity. During warm days in my basement orchid greenhouse I lightly wet all my plants in the early afternoon when temps get near the max (85 f). This usually jump humidity by 10% and also cools the room a couple degrees (evaporative cooling). I agree misting a plant in a large room is pointless however (unless you are wetting copious air roots also).
Mistking
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