The main difference is that with Section Access, you can keep everything in one file which has advantages as long as the file is published only on one place on the server. But if you allow people to download it, you have a file that is larger than it needs to be, and you have compromised security - the file is not encrypted and contains data that the user isn't allowed to see,
The Publisher loop-and-reduce has the advantage that you now have many files, each containing exactly what it should. This is tremendous advantage if you want to publish the files in different folders on the server, or if you want to allow downloads.
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