Zend certified PHP/Magento developer

when Magento will use catalog product flat table

I have not enabled the Use Flat Catalog Category and Use Flat Catalog Product in the admin panel. But when I checked the Database Magento created the flat tables.

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Can you please give me a brief on the below things (if possible examples)?

  1. What is a Flat Catalog?
  2. When it will create Flat Tables?
  3. How Magento will use this Flat Table (EAV V/s Flat) even though the flat option is not enabled?