Paseos y Rutas a Caballo por Sierra Nevada
El uso de los tres latiguillos es un misterio para muchos. la explicación, una de ellas, en la wikipedia, por supuesto en inglés, use of billets:
Use of the billets
Most jumping saddles have three billets. This not only allows the rider a spare should one break, but can also provide an adjustment option. For horses on which the saddle sits nicely, neither slipping forward or back, the first and third billets should be used. On horses where the saddle slips back, the first and second billets should be used.
The second and third should never be used together, as they are attached to a single piece of webbing to the saddle’s tree. Since the first billet is attached to a separate piece of webbing, you can safely combine its use with either of the other two billets.
There are other girthing systems available such as the Adjustable Y system or a similar girthing system. These also provide an adjustment option and have a front girth strap which is connected to the saddle tree point, and a rear girth strap giving it a Y shape and stability.