[KeytarHero]

At small venues it's often just because the band is playing loudly. Some drummers play pretty loudly, some guitarists play amps that sound better with the volume cranked, and then singers are going to want the vocals louder in the monitors so they can actually hear themselves over the loud drums & guitar.

If stage volume is loud, the sound guy is likely going to push the volume even louder, both so that he has some level of control over it, and because sound coming off the mains is going to sound a lot clearer than if you're hearing everything off the stage monitors and then reflected off the back wall (yes, even if that means things are louder, they can still be clearer).

[ashark]

Interesting. I find it hard to imagine that the reflected sound from the wall could be worse than the ear-against-tv-speaker-volume-at-full-tuned-to-static effect that ~2/3 of small venues I've been to end up with, but that does explain the motivation for it, at least.

[KeytarHero]

Well, in most cases the stage volume is already in so-loud-you-lose-clarity territory, so the clarity you gain from the sound guy turning up the mains a bit is worth the clarity you lose due to the extra volume. We're not talking massive increases in volume here.