On the Herald's Staff

5.9. Any herald on official business may carry a small white stave to indicate they ought not be interrupted.

9.2.3. When announcing a multi-field, multi-herald tourney a herald’s white stave may be raised when speaking to assist in prevention of overlapping calls.

The above are quotes from the Lochac College of Heralds official policy. It is rather brief on the point, giving it as simply a method of stopping interruptions during calls. However, there are a great many uses for the herald's staff, and they are currently greatly under-used by heralds in my experience.

The most useful area of heraldry in which a staff can serve well is in tourney heraldry. At the start of a bout, the marshal indicates each fighter as they're introduced, and each fighter usually indicates the other with their weapon. If carrying a staff, the herald can join in on this. At the end of the bout, one fighter is again indicated, the victor, and if carrying a staff, the herald can help with this. Also, the staff can be raised to call for attention. In a multi-field environment, this attention is, as indicated in the Lochac policy, quite useful from the other heralds present. In a single-field environment, raising a shining white staff can raise the visibility of the herald, particularly if it's crowded.

Outside of tourney heraldry, a staff has some other very important uses for a duty herald. Firstly, it increases the visual impact of a herald in their tabard, adding to the style and pageantry of the event, which is, after all, one of the important roles of the herald. Secondly, it gives the the herald's hand something to do, rather than fidgeting or scratching (though, be careful not to drop it too often once you inevitably start twirling your staff).

Finally, when making an announcement in a hall, or calling for the beginning of court, a stout staff banged on the floor before your 'Oyez' makes it slightly more likely to get attention, and on top of that, adds an interesting note of class.