Hiya Jason!
 > oh, I understand the difference, but does that mean that a guitar amp
-> needs to be at full volume (or a little more) to get the desired
-> sound?
 Well, for some or many guitar players you need to set the amp up to be
wide open and use a master volume control for overall all gain control.
One guitarist I know runs the amp full out and has an attenuator on the
output itself.. it's an old Fender Virbalux, a smaller brother to the
Fenter Twin Reverb.
 -> when I tell people in a band to turn their amps
down and let me take -> care of the volume am I doing them a disservice?
Could be for two different reasons. One thing that I've always known to
be true is that if the sound doesn't cut it for the band, and if they
aren't able to hear everything and everone then they can't get that
"magic" going that musicians are often able to do, and without that
magic, nothing else is worth bothering with to get to the audience. Then
also for the guitar players, they should be able to get a good sound at
a reasonable level so that micing of the instruments and then doing the
blend through the sound system is possible.
Bonnie *:>
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