Homes in places where there isn't much rain or snow usually don't need gutters, since the amount of water that falls along a roof isn't significant enough to need them. Some homes with particular qualities do not need gutters. A house without a basement or a house with excellent landscape drainage may not even need gutters. Rain can fall from the roof of the entire house and slip off the walls, thanks to gravity.
Homes built according to the code are located on a slight slope to keep runoff away from the foundations. If rain falls from the roof because there are no gutters, the water causes massive erosion, dragging more and more dirt away every time it rains. This causes the carefully sloped landscape to wear away, allowing runoff to flow into your home instead of away from it.