i always set my individual faders at zero.
i set my INPUT (either from my card, or other device) in such a way as to get a very clean input level,
where i'm seeing RMS of anywhere from -12 to -22.
if you are tracking individual input at -18, and your faders are set to 0, you still have tons of headroom, and when you go to mix a bunch of tracks, where you THEN set your faders in relation to the output at the master bus, is all that really matters.
point is, at EVERY stage of inputting level to track, you have to consider what you will do to that track in the future...
if you never applied any fx or eq, you could run with it a bit hotter...
but you want HEADROOM to be able to further process later.
as soon as you set up a send for a reverb, you are pushing more gain into that channel that is feeding the master bus, and after 40 tracks, that gain starts to add up to distortion very easily if you are not careful.
it is easy to raise level to be heard,
it is hard to turn down signals that were captured TOO HOT