メリット

• Removes need for large disk space or memory allocation to generate zips, even huge zips. So it works on Heroku.
• The user begins downloading immediately, which decreaceses latency, download time, and timeouts on Heroku.

References

• zipline - A gem that lets you stream a zip file from rails
• S3から複数のファイルを取得しつつ on-the-fly でZipを作ってブラウザに返す