Cell Load Sharing [CLS] is a feature used for off-loading cells experiencing high SP-TCH Congestion. By using this feature, it is possible to reduce Handover Hysteresis so that calls are Handed-over to other cells [Which will not be done if Hysteresis was constant]. Certain parameters allow this reduction in Handover hysteresis when a certain amount of resources in current cell are already occupied.
By the way, the percentage reduction of Handover Hysteresis is also configurable and the Hyst is usually Ramped-Down with time.