Comment by donavanm
It's a much more direct/efficient connection from the EC2 instance to the S3 storage servers through the virtual network layer. It reduces the network path/length through the AWS network _and_ removes the number of virtual network functions/servers (ala "LB") that your connections will traverse.
That's helpful to know, thank you! I'll take a look at that and see if it improves S3 performance.