It
depends on the music and the venue.  If possible, using
 amplifiers for the guitar and bass is more ideal -- the musicians
 will have more control over their sound and not have to rely on the
 sound person, and
 this is a good thing. 
 Not if you are the sound guy.  One of the more common annoyances was
 guitarists with Marshall stack(s) who have more power than the
 entire PA
 and won't turn down so that people can hear the rest of the band...