USB 2.0 provides a bandwidth of 480 Mbps. USB 3.0 (aka “SuperSpeed”) provides 4.8 Gbps - or 10 times the bandwidth of USB 2.0.
There are other differences between the two but this is the one that’s important to camera performance. This factor of magnitude level of improvement in bandwidth is beneficial for carrying 1080p-30 video from the camera to your PC. 1080p-30 at 24 bit color depth requires approximately 1.5 Gbps, which does not fit within the USB2.0 bandwidth and therefore video must be compressed by the camera itself before being sent over the USB connection.
USB 3.0 allows the camera to send uncompressed video over the USB connection to the PC where the PC's better equipped hardware and software can be brought to bear for better final compression performance over the web connection during a call.
USB 3.0 does bring with it some restrictions. As with HDMI, this higher bandwidth requires different cabling than its predecessors. USB 3.0 will only work with USB 3.0 ports on devices and with USB 3.0 cabling and extenders.
Some USB 3.0 cameras are USB 2.0 “compatible”, which means that they have the capability to recognize a USB 2.0 port or cabling and downgrade to a low resolution video stream (e.g. 640x480, 1024x768, 720p-30- 16bit). In this case, you would probably be better off with a USB 2.0 camera.
Most modern laptops and PCs have been shipping with at least one USB 3.0 port for some time now.