You can run more plug-ins with lower latency inside the DAW using USB 3 compared to FireWire. Generally, USB 3.0 has 5 times the bandwidth FireWire 800, and up to 10 times that of USB-2.

FireWire Limits you to 55 stereo UAD plug-in instances at 44.1kHz and 512 minimum sample buffer. USB 3.0 does not incur this added buffer, and hundreds of plug-in instances can be run (depending on available DSP power).