In a live playing situation , the rule of thumb for setting the volume on guitar and bass amps is simple - NEVER play louder than the drummer's acoustic stage volume. If all the instruments are set to the same volume , it's an easy task to mix the band's sound "out front" .... you know- where your fans are . This works in most situations .
In very small venues , most bands mic only the vocals and the kick drum , which works pretty well . Personally , at smaller venues , I still mix a bit of guitar in the PA . Here's why - guitar amps are very directional . The sound coming out of the speaker cab pretty much travels in a straight line , and does not disperse throughout the room . Folks sitting on axis with your amp will hear you , people sitting on the other side of the stage won't hear you as clearly ... sometimes not at all . Micing the guitar amp and adding it to the mix is the only way to evenly disperse the guitar sound throughout the club ... without cranking the amp up too loud .Plus ... many of my guitar playing pals suffer from hearing loss and tinnitus, which is a permanent ringing in the ears ... SAVE YOUR EARS !!! NEVER play louder than the drummer !!
This "never play louder than the drummer" concept works well in medium and large venues , too . In medium sized venues , I might not add the bass to the mix much , if at all . The reason - bass guitar sound is non directional - it will fill the entire room with it's sound - all by itself . In large venues , all the instruments are mic'd up and added to the mix .SIMPLE !!!
Here is a youtube video link of my most recent band. In this video , I'm using a lunchbox size Carvin V3M tube amp . It's set to 50 watts . The audio guy at the club asked me to turn the amp way down ... it ended up on "1" !! I trusted this fella , and sure enough , my guitar sounded like Thor's Hammer out front . He also added some guitar to my monitor mix , and I had no trouble hearing myself !!