Volume Staging Methodology and Impacts on Audio Quality ?

Hi,
 
Coming from an analog background I'm still trying to learn some fine details of DAW theory.  One subject that entered my mind was the notion of what I will refer to as Volume Staging.  For example, multiple guitar tracks feeding a guitar bus feeding a master out.  What are the audio quality impacts of volume (fader) alterations at those three stages?  Are there any rules of thumb to be followed in order to reduce potential negative impacts to audio quality?   I've heard some people claim that volume levels have no impact on audio quality where others say any deviation from 0dB can impact audio quality (and the more stages where alterations occur the worse the potential impact).
 
Thanks for any insight,
 
      Sonic

Actually, it's best if nothing even gets close to 0 dBFS.
 
For a long time, I assumed that because all internal processing was floating-point (which cannot clip) that it wouldn't matter if the master bus (or any other bus) was getting hit too hard. You'd just turn down the input gain on the bus and carry on. Turns out, there are a lot of plugins that don't behave well with values > 0 dB, and distortion can in fact occur.
 
The main psychological adjustment going from analog to digital is getting over the deep-seated notion that signals need to be as hot as possible all along the signal chain. Digital audio is so clean that even very quiet tracks can simply be brought up without penalty. Sure, you do still get a raised noise floor but the SNR is so huge to begin with that it rarely matters. You can easily add 30 dB of gain to a too-quiet track and still end up with a better SNR than high-quality tape.