When we talk about the heaven/earth/man of the garden, we are referring to the overhead elements/ground plane elements/connecting elements. Every garden requires this balance of the three.
The overhead can be represented by trees, whose canopies shade and protect us. It can also be an arbor that stretches over a seating area.
The arbor gives us shade, and more importantly a sense of safety and cosiness. It need not have plants on it, though that is an attractive way to add to the shade and eye appeal, and it does not have to be solid. We find that people will congregate under an overhead element in a way that doesn’t happen in open seating areas.