For the same reason that the south side of hills are warmer, the south side of buildings are, too. The sun strikes the south side of a house more directly for more hours than other sides. The heat reflects down to the ground near the wall, warming it.
Light as well as heat reflects to plants on the south side of a house, especially from light-colored walls. This is a good location for heat- and light-loving plants. The ground next to the south side of a house gets more hours of sunlight a day, as well as the extra light reflected from the wall.
On the other hand, the heat in this location can be brutal in the summer, frying all but the most heat-tolerant plants. In areas with strong summer sun, it may be difficult to find plants that grow well on the south side of the house. A large tree on the southwest side of the house will shade the south wall, as well as the roof and the west wall of the house, keeping the house cooler as well as creating a cooler microclimate there. Vines on the wall cool the south side of the house without shading it.
The north side of a house is dark and damp in the cool months, but shady and pleasant in the summer. This is a good location for shade-loving annuals like impatiens. If you plant a tree on this side of the house, select a deciduous tree so the bare branches will admit light in the winter.
East exposures are ideal for shade-loving flowering shrubs and perennials like gardenias and azaleas, which bloom best with lots of light, but can’t stand the heat of the afternoon sun.