Low sample range can cause jagged-edged shadows.
Higher sample range causes soft-edged shadows.
Large values extend the area that is averaged, effectively bringing the edge of the shadow outward, producing softer-edged shadows. Soft-edged shadows have more antialiasing. The effect is somewhat like the falloff of a soft-edged spotlight.
The default Sample Range value is 4. The Sample Range value can be any floating-point number from 0 to 20. Values of 2 to 5 are recommended. Values below 3 can produce coarse-edged shadows. You can reduce this effect by increasing the map size.