One interesting thing about S3 is the vast scale of it. E.g. if you need to store 3 PB of data you might need 150 HDDs + redundancy, but if you store it on S3 it's chopped up and put on tens of thousands of HDDs, which helps with IOPS and throughput. Of course that's shared with others, which is why smart placement is key, so that hot objects are spread out.