I’d actually go even further and say that the only appropriate time to use -Werror is when running tests for code that hasn’t been merged yet… once it’s “released” you don’t want to use -Werror any more.
Ditto automatically running unit tests/etc too. (Perl is actually a major offender here… last time I used Perl, installing a module from CPAN would run its unit tests by default. Why do I, some random person installing this module, care if the tests pass now? The tests should have been run prior to this being published! I have horrible memories of the DBD::MySQL package failing to install because it ran tests that assumed localhost was running a MySQL server with anonymous auth enabled and the whole module failed to install if that wasn’t the case.)