COPR uses this option.
IIRC it's used to fetch only partial metadata.
[dnf.git]$ git grep enabled_metadata | wc -l
[dnf-plugins-core.git]$ git grep enabled_metadata | wc -l
This bug appears to have been reported against 'rawhide' during the Fedora 25 development cycle.
Changing version to '25'.
*** Bug 1357797 has been marked as a duplicate of this bug. ***