There's a lot of confusion out there regarding levels and digital recording, and most of it stems from the fact that there's still a ton of people around who cut their teeth recording on 16 bit systems. So you still hear people talking about stuff that applies to 16 bit systems even though with 24 bit (or higher), it doesn't matter. In a 16 bit system, it was advantageous to have higher levels because you started to lose resolution with lower levels. This is still technically true with 24 bit systems, but within the range we're talking about, the difference in resolution is completely negligible.
You don't really gain anything by recording a track a -12dB compared to recording it at -20dB anymore. In a very real sense, it's better to record everything a bit lower because it gives you more flexibility while mixing. I know people who are going to school for recording, and they're still being taught that they need to record so they are just below clipping... They spend forever setting input trims and messing with analog compressors before the converters (the compressors themselves aren't necessarily bad if you sure that's what you want). I just think people a lot of people are still clinging to this outdated information, and that's still be passed down as gospel to beginners... It's madness! :-)