Well, my understanding (and common advice) is actually not to water the leaves at all if possible as that has no benefit apart from helping diseases set in.
You can damage the plant if you water leaves in bright sunshine, because water will act as a lens and leaves will get burned. Otherwise I'd follow nature: plants get water when it rains, so leaves should have some water too.
Depending on the species it may make sense to raise the humidity in the air (that's especially valid for indoor plants or tropical plants in greenhouses, hence misting). But watering the leaves is not needed and is pretty much useless to the plant. In nature of course plants get wet under the rain but, as mentioned, this helps diseases (moulds, mildew, virii, etc) take hold so in general it's best avoided if at all possible.
