I just don't understand why guitarists do this. Is it an ego thing? Are they deaf? I've been to at least two auditions at which a guitarist was silly loud, one of them half-deafening me for days. In both cases I asked if they always played at this volume and when they said 'yes', I immediately walked.
I can't be doing with these fecking wunkers. This behaviour is selfish, stupid and very unprofessional. But at least it does have the advantage of letting you know immediately what sort of tosser you're dealing with, thus saving time.