I had no idea there were such things as audiophile ethernet cables, but apparently they exist. Why? Some people feel they sound better. Yes, I know, it’s just data they are transmitting, not analog audio signals. Regardless, they have their adherents.
They get tested against each other in detail over at ARS, which you can read here http://arstechnica.com/gadgets/2015/07/even-vegas-strangers-agree-340-audiophile-cables-make-no-difference/
tl/dr version:
Let’s get this out of the way first: the overwhelming majority of subjects could not tell the difference between a $350 AudioQuest Vodka Ethernet cable and a $2.50 “Cable Matters” cable from Amazon under our specific testing conditions. I don’t think anyone was expecting anything different from this test, including the true believer audiophile set. However, it’s possible that our test didn’t account for some variables—which means, at worst, our results aren’t broadly applicable.