well, of course, we are strictly talking MY interpretation here.
there are no CORRECT answers, only opinions!
LOL
that said, when i want big fat rock sound, i track a single big fat rock track.
then, on playback in the mix, and ONLY then, do i decide if it needs more.
typically, i'll track with two different guitars, two different amp setups, two different mics, maybe even two different rooms! then i'll mix them hard left and right.
there is a clarity there, and the power comes into the way the different sounds spread out across the sonic spectrum.
at least, thats something i'm going for with my own material, and other folks' productions......
then, it's down to the performance. are the two guitar parts really gelling? performance wise? do they groove? are they totally brain-locked into the same power mode!!?
that's what i dig.
now, if you look at it the way brian May (Queen) used to layer tracks, it's a different function...
he was not playing the same part multiple times.... he was multitracking individual parts to create the whole.
like scholz with boston, or anybody else from the classic rock days that layered guitars to create a bigger picture.
but the more you layer a single rock rhythm part on top of itself, the more the sound itself gets diminished.
you can only occupy so much sonic space with one part, before it starts to lose all of it's clarity, and it kind of mushes together.
we're talking aesthetics here, i'm sure there are pro producers who regularly multitrack the same rhythm guitar parts on top of each other, and make it work.