Fooman, you're right that getting the proper tone manually is frustrating for the artist, and that vibe/mood is important to keep. I recently spent two hours working with a guitarist who not only was easily distracted and not very patient, he also had no knowledge and understanding as to
why things were taking so long. That's equally frustrating for me, because I'm not only working hard to get the right tones for the tracking, but meanwhile keeping him from getting impatient and not wanting to be there.
But there is another reason for doing this.
In the way I have my studio set up, I have a large set of speakers powered by a Pass-350 amp that can be used to crank up while he tracks his guitars. This is similar to him working in the same room as both of the amps (bi-amp in two separate rooms), mixed to taste, and he's digging the tones. This really helped his performance and he played with some serious conviction.
It's a bonus that I can offer guitarists and bassists in that they don't have to wear headphones while tracking, AND they can be mic'd from another room. It's a win/win for us. So, any amount of work getting us to that point pays off when the artist is actually tracking and burning the place down with massive overtones. It's pretty real.
I should also point out the win for me. Since these are the same speakers I master on, (and sometimes mix), if the sounds we're getting from those make me feel right, then mixing the guitars later is incredibly fast and requires little to no additional processing.