It's an endless battle of visual feed back, you look at the console meters and they're pegged. So that is wrong. But then you look at your PT session and you've got "good strong signal" on the dBfs meters. If you track using console meters everything looks great on the desk, then you look at your PT session and all the dBfs meters are "weak signal".
Studio engineers that came from analog and went to digital usually have a good understanding of what "level" is. They can look at a digital meter and see -16db signal and not think twice about it because 0vu is -16 (or -18 or whatever), but an engineer that grew up on PT wants to get that signal as close to digital 0 as possible because that is what their visual feedback is telling them to do. They never had to align a tape machine and truly understand what "level" is.
A great engineer once told me "as long as the needles are moving, your fine" referring to VU meters when tracking.
The same engineer sat me down and explained to me the whole "using all the bits" thing. He broke it down into math, I don't remember the exact numbers (so correct me if I'm wrong) but it's something like on a 24bit recording you have to get 128dB below digital "0" before you can hear the low resolution breakup of "the bits" on 16bits is like 96dB below "0". So you don't need to get up to 0dBfs to "use the bits".
good quote "you can have your 24bits, my tape machine has billions of bits" ;D
Ultimately it comes down to gain staging and fader resolution. If your going to stay in the box then yeah, you can track all the way up to digital 0 and start pulling down your faders to keep the mix buss from clipping your converters. I know the software can handle hundreds of dB of headroom, but when it comes back out to the analog world, your converters are still abiding by analog rules.
I personally just listen, if I'm tracking drums I put all the faders at "0" and adjust my input levels until I have a drum mix that sounds good. If the hi hat is peaking at -30dBfs, I don't care. It sits well in the mix with my fader at unity gain. I'm not going to crank my preamp to get level up to digital 0 so that I can just pull down the fader to -30, it makes no sense to me.
I want to hand a PT session to someone and when they open it up all the faders can be at unity and they already have a basic "mix" going with levels. I print the level that sits well in the mix, not the level that visually looks the best. Is that bad? Well, I've NEVER had anyone complain about signal not begin "strong enough" in my sessions. So.... I guess it's ok.
JUST USE YOUR EARS!!! If it sounds good it is good, reguardless of what level it is!