| They have a two fold benefit: 1. They are adjustable for fine tuning. 2. If you have ever removed a timing belt without some how locking the cam gears in place you know that the force of the valve spring will snap the cam around easily. When running higher pressure valve springs (required with some aftermarket cams) this pressure is high enough that it will "snap the cam around" while the engine is running. This is transfered forward to the VTC gear. The internal spring is overwhelmed and the cam rotates until it hits the internal stop then it rotates back as pressure is remove from the cam lobe. This produces an extremely annoying rattle from the VTC gears. The BDE cam gears have a higher pressure internal spring that can take the abuse from the higher pressure valve springs and eliminates the rattle. Brett can probably explain it much better than that but that's the gist of it.
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