Toyota Hilux 2008 Pulley Balinera Anternator

Dear friends.
I am writing to make the following consultation, the pulley of the alternate pose a Balinero that has a function that press in a sense of rotation and releases in the other, causing the alterant to turn in one sense and in the other not.
The question is as follows, which is the objective of this mechanism, if in all the cars that has seen the alternator's steering wheel is fixed and has nothing inside.
Perhaps the people of Toyota invented that to earn more money, I don't see meaning to this mechanism. The balinera is at approximately $ 300.
Kind regards.

Good compi. I tell you, this pulley is commonly called Alternator Hydropolle, it is designed to remove the vibration from the belt that in the case of your car is serpentine, I mean, it carries a single long strap for everything, instead of individuals for the water pump, alternator, air conditioning and hydraulic direction. You are going to see this in the diesel engines and some other gasoline. The price depends on each country but here in Costa Rica is in the 350 dollars. It is designed to function from about 80 to 90 thousand kilometers but then there is nothing left but to release the wallet, since if it is fixed, do not remove the vibration of the system and cut the strap or break your tensioning arm.