I think covering is very important, at least with coleus cuttings. It helps retain humidity which, in turn, encourages rooting. Outside in summer heat, you might need vents to let heat escape. But here, in summer, our humidity is generally high enough to not need the cover.
I always use a lid in winter in the dry air of the house. And use moist, not wet soil. Too much water can cause rot. With a humidity dome, they rarely need additional water after sticking.
Karen
