Hi Majo,
At this time, I believe that may be all the documentation we have for Amazon S3 (I cannot find any additional notes). Documentation tends to be written by volunteers, and it appears no one has found time to enhance the documentation, etc.
I believe files are directly uploaded to S3, and a local copy is only written temporarily until the file uploads to S3. But, I may be mistaken. So, hopefully someone who uses the Amazon S3 plugin will respond to correct me if so.
Tim