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. Erosion also causes the base to settle. The gutters control the water that reaches the roof and direct it to a single flow that moves away from the house.
Without gutters, water runoff may build up around the house, enter the foundation, and cause water damage over time. Gutters cannot effectively ward off water unless they are cleaned frequently, and damaged gutters can cause more damage than not having gutters, since they can cause water to accumulate along the roof.