It will probably sound better and you will have less feedback problems. The same principle applies for cutting. In general, cut the frequencies that are too loud. If a voice has too much bass, first try cutting the bass rather than boosting the highs. If you have a mid-control, you may achieve a better result by gently adjusting two adjacent controls rather than drastically cutting or boosting one control.
Tone controls affect a broad band of frequencies.
Excessive boost or cut may degrade the response of a microphone or instrument. A slightly lower volume may actually be better than an unnatural sound caused by too much EQ adjustment. The system equalizer is designed to do that job. You need to make sure your speaker system is properly designed, installed, and adjusted. Also, the tone controls cannot improve the acoustics of a room.