It's sneakernet optimized to deliver direct to S3, with full end-to-end integrity checks. Depending on the amount of data you have and your internet connectivity, this can be significant optimization — for example, say, you work with professional photography or video but live in the United States where only a small fraction of people have an uplink speed greater than 10-30Mbps even if their download speeds are 500+Mbps. If you can generate 8TB of data in less than a month, this is faster and doesn't interfere with all of your other network usage.