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They provide a warranty and a proven level of build / material quality. Beyond that Monster cable is no different to perhaps a good cable you might find elsewhere for less. The thing is finding that cable for less which isn't badly built. Monster is like Sellotape I guess - you can buy perfectly functional tape for less, but Sellotape is a 'name' you can trust to be measure up to a certain level of quality and support. Same goes for Monster. If they sell what you want, I say buy it and get it over with - unless you want to DIY a solution.

Are higher-grade cables worth it in terms of sound? No - absolutely not. Provided the cable is not total crap and it's put together properly which is what you can expect of a mainstream brand, any genuine difference in the sound due to a cable is due to characteristics in a cable which shouldn't be there in the first place.
 
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