As compilers change they can end up adding new warnings to the defaults, or for or example -Wall, or -Weverything. And different compilers might throw different warnings on the same code with the same options involved. Using -Werror will force an error, which can end up terminating the build for users, even when the code compiles cleanly on your version of your compiler.

So -Werror is fine if you are shipping binaries, but if you are shipping source code, it's probably a good idea to not use it in the public build system.

What's the difference if compilation stops at the warning? You'll (or your team, or whoever) fix it anyway, and if you won't, you have a people problem, that must be solved at the policy (or HR) level.

Solving people problems at the tooling level is a certain way to get unintended consequences and alienate the good people that weren't part of the problem. Of course, you can get some tooling to support your people, but tools to police them are worth less than zero.

Anyway, unrelated to that, I do like to live warnings on code that is not ready to production. It's an easy (effortless in fact) way to make sure it'll be fixed before deploying.