The problem with this setting is that a warning from GCC may mean some totally trivial thing that does not really affect code correctness, or it means something you really want to fix. Setting -Werror will then cause both of these to make your compilation fail. You can make it more finegrained, really per warning type, but then you get a really long list of options.
Also, new GCC versions typically add more warnings, or make existing checks stricter, so after a compiler upgrade you often get lots of errors if you have -Werror.
So in principle a useful option, in practice it gives you a lot of busywork.