The theoretical throughput improvement offered by USB 3.0 is dramatic – a theoretical 10X jump over existing USB 2.0 hardware. USB 2.0 maxed out at a theoretical 480Mbps, while USB 3.0 can theoretically handle up to 5Gbps.
The beauty of USB 3.0 is its backward compatibility with USB 2.0; you need a new cable and new host adapter to achieve USB 3.0, but you can still use the device on a USB 2.0 port and achieve typical USB 2.0 performance.
The benefit here is that USB 3.0 is a powered port, so you don’t need to have another external power supply running to the drive (as you do with eSATA; unless the eSATA drive you’re using is designed to steal power from a USB port while transferring data over the eSATA interface). link.