ORIGINAL: mixsit
...You might be safe to say less gain works live as well. No one in the audience hears the dynamics and tone of the amp from three feet away either...
Live sound is a whole different world, especially for heavy rock.
For one thing, the human ear hears very differently at rock-concert volume than it does at typical home listening volume. A guitar that sounds flat, weak, and fizzy at 83dB may sound massive and roaring at 110dB, in part due to the Fletcher-Munson curve and in part due to to the physicality of the powerful sound waves literally rocking your body.
For another, rock concerts typically have a *very* high ambient noise floor. If you have 90dB SPL ambient noise (shout to be heard levels) and you dial up a guitar sound that is swinging 18dB VU on chugging palm-mutes, then unless you are running with RMS levels into the pain threshold, all the detail and sustain from the guitar is going to get lost in the crowd noise.
I don't disagree that many heavy rock guitar players are overly gain-happy both live and in the studio. I think a lot of it comes from a tendency to play solo through headphones or nearfield speaker playback, where you get an exaggerated sense of detail and clarity. Push the listening speakers back a few feet, add in some bass, drums and splashy hi-hats, and turn the guitar level down enough for the vocal to squeeze through, and all of a sudden that massive guitar sounds like weak midrange fizz.
But even still, there is very often a significant difference between what works in the studio vs what works live. The players will have built a sound and an approach focused towards live performance (which is what they do, after all). It is the job of the engineer to find the most flattering way to capture and present the experience of the musicians' performance in a way that will translate well in real-world playback.
Cheers.