The PreventIntersection property is used to avoid overlap between series labels and overlap with rendered values and axis borders. By default, the PreventIntersection property is set to false, which causes series labels to overlap, making them ugly and unreadable. The image below is an example of a chart with the PreventIntersection property set to false.

Series labels will not overlap if the PreventIntersection property is set to true. The image below is an example of a chart with the PreventIntersection property set to true.