Non-fleeing units comprised solely of models with this special rule add their number of Full Ranks after the first one to their Leadership (up to a maximum of +3). This rule cannot be used to modify the Leadership that is distributed by models with Inspiring Presence (but the received Inspiring Presence can be modified by Safety in Numbers).
Furthermore, if all models in a unit have this special rule, this unit gains a +1 modifier to its Flee Distance rolls.