...--acl public-read makes your files publicly readable (make sure your bucket settings are also set to public). --follow-symlinks won't hurt and fixes some weird symbolic link problems that may come up. Most importantly, --delete permanently deletes files in the S3 bucket that are not present in the latest version of your repository/build. If you're uploading the root of your repository, adding --exclude '.git/*' prevents your .git folder from syncing, which would expose your source code history if your project is closed-source. (To exclude more than one pattern, you must have one --exclude flag per exclusion.