The USB port on the camcorder is USB2. If you are doing large transfers and have a built in SD reader in your laptop or desktop computer, it will be much faster to take the microSD card out of the camcorder, place it in an SD adapter, and read it from the built in SD reader. Of course if you are simply using a USB2 SD reader attached to your computer, then there is no point removing the microSD card from your computer.
In a test on my MacBookProRetina, 2.85 GB of files were read from the GW77 using the USB cable in 4:11 (4 minutes and 11 seconds), while if I removed the microSD card and used the built in SD reader on the MBPr, it read the files in 1:00. Note that the the MBPr has USB3 ports, so the bottleneck is the USB2 interface on the GW77.
Recently I transferred about 48 GB from a 64 GB microSDXC card to my computer. It took about 17 minutes using the SD slot on the computer. If I had used the USB cable to the GW77, it would have taken well over an hour.