The dampened pulley is not to quiet chatter of the flywheel/ clutch assembly spinning in the bellhousing. It is to quell engine harmonics (especially major criticals, of which every engine has one or more at various RPMs- keep an engine at the major critical RPM long enough and you can snap a crank).
Porsche never installed a harmonic damper on these motors until the M97 3.8. As soon as you remove the dual mass flywheel, there is now NOTHING to dampen ANYTHING. Adding the harmonically dampened pulley allows for some damping factor on the engine, which when running a single mass flywheel, is pretty important in my opinion.
As to the pros/cons regarding the added weight of the dampened pulley, that downside falls very distant compared to the pro of adding engine reliability/ longevity.
If anyone would like further reading about harmonic dampers, Steve Dinan has an excellent section on his site, referenced with the following link:
http://www.dinancars.com/bmw/technial-info/the-dangers-of-power-pulleys-and-understanding-the-harmonic-damper
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