Integrating your AWS account with your HotRiot account will normally result in a reduction in data transfer usage. In this case, HotRiot will be storing and retrieving your document files from your own S3 account. As a result, HotRiot will not include the bandwidth required for serving this content as part of your monthly data transfer usage.
This can have a profound impact on the data transfer usage for apps that process document files. Of course, AWS S3 has storage and bandwidth charges of their own. However, AWS only provides raw service, so their charges are far lower than ours. Please see the AWS website for details.