We admit it, we love to hear a cranked up guitar amp, a thunderous bass, and hammering drums — there’s nothing like it! But volume can very easily get out of hand, leading to a volume war onstage. The guitarist can’t hear herself, so she turns up. Now the bass player can’t hear himself, so he turns himself up. The drummer plays louder in response. Which leads to the singer not hearing herself, and when the monitors are turned up, everything erupts into eardrum-bursting feedback.
While it will help to try to position players and their amps/monitors so they can directly hear themselves without getting blasted by another player or players, the only real way to prevent volume wars is to get everyone onstage onto the same page: set the volume to a comfortable level where everyone can hear everyone else and realize that there’s more to playing music than just hearing yourself as the loudest source onstage. It’s really about being a team player and having consideration for your fellow musicans.
Using guitar feedback as an effect can be great; onstage howling feedback from excessive volume never is. Always be aware of the volumes of the other instruments around you, and if you can’t hear yourself, rather than turn up, ask everyone else to turn down.