I was wondering the same thing. It isn't the easiest thing to plug in -- I have to actually pay attention when I do it and I feel like I'm going to break a pin one of these days.
I talked to a guy at the Samsung store or whatever you call it inside Best Buy and he said the new cable provides a faster charge ( I've checked and it's been true so far it's provided about a 35 to 40% faster charge rate than the standard micro usb) and a faster data exchange rate as well. Haven't jtested that just yet.
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I believe it charges the phone faster similar to how the Lightning cable works for the Iphone 5 and above. Also faster data transfer if you hook it into a USB 3.0 port on your computer.
The quick charging has to do with the Snapdragon fast charging feature, not the USB 3 cable. If I use the cable from my LG G2, it charges just as fast with micro USB.