A unit that is accompanied by a Leader may re-roll failed Leadership tests in the following scenarios:
March when within 8" of enemy units.
Redirecting a Charge.
Reforming from Defeat after losing a round of close combat.
Restraining from Pursuit
Swift Reform (see Musicians)
Some Leaders also have the option to take specialised equipped. If this is the case, it is clearly stated in their entry in each separate army book.