The project I work on (QEMU) uses -Werror in development but defaults it to off for releases. This means that warnings don't sneak into the codebase but end use

The project I work on (QEMU) uses -Werror in development but defaults it to off for releases. This means that warnings don't sneak into the codebase but end users don't have to deal with unnecessary build failures just because they're using a newer and pickier compiler or oddball host system. Putting in the effort to get down to "emit no warnings" (and then enforcing that you stay there with -Werror) is worth doing exactly because you then do get new problems drawn forcibly to your attention, IMHO.