What is the difference between `Allowed` and `Enabled by default` in Syndication?

The template /RSS seems to work only when both Allowed and Enabled by default are checked.

  • Allowed: Allow syndication for collections and folders on site.
  • Enabled by default: If syndication should be enabled by default for all folders and collections.

If one of them is not checked /RSS doesn't work.

To reproduce it:

On the other side I cannot see any difference by the setting Show settings button:

  • Show settings button: Makes it possible to customize syndication settings for particular folders and collections