Decision to use Custom Controller rather than Controller Extension

Question

I came up with one question which asks me to select two options. Question is: When would a developer use a custom controller instead of a controller extension? Options are:

1. When Visualforce page needs to replace the functionality of standard controller.
2. When Visualforce page does not reference a single primary object.
3. When Visualforce page should not enforce permissions of field-level security
4. When Visualforce page needs to add new actions to a standard controller.

To me correct answer is: 2 and 3. But it is telling the correct answer is 1 and 3. Just wanted to check here if my understanding is wrong.

The reason why I don't want option 1 is that with controller extension we can always replace the default functionality of standard controller like custom save in controller extension.

Answer 1

According to me answer will be 1 and 3.

Controller extension leverages the built-in-functionality of Standard Controller, but overrides one or more actions.

Where as, Custom Controller replaces the functionality of Standard Controller without leveraging it.

There is a significant difference in between leveraging and replacing.

Also, think about that, a class to be recognized as controller extension it must have a constructor that takes a single argument of type ApexPages.StandardController or custom controller you want to extend.

For more information, refer What are Custom Controllers and Controller Extensions?

Hope, it makes sense!