Volume Booster Use at your own risk. Playing audio at high volumes, especially for a prolonged amount of time, can destroy speakers and/or damage hearing. Some users HAVE reported destroyed speakers and earphones. If you hear distorted audio, lower the volume (but it may be too late).
When you set the boost to zero, Volume Booster will be off. The notification icon is just for ease of launching. If you don't like seeing the notification icon when Volume Booster is off, just go to Volume Booster's Settings and set it to appear only when Volume Booster is running.