Originally Posted by Greg Reierson
If you're working at 24 bits or higher it really doesn't matter that much. If your peaks are at -20 dBFS that still leaves you 124dB to work with. Probably enough.
Just leave some headroom without having to use a limiter and you'll be fine.
Rare From Mastering
Agreed, keeping in mind that if you're talking DVD, you don't have the same leeway as if the final destination is CD. If the source files are 24-bit and they're going to end up on a 24-bit DVD, you don't want the sources to peak at -20dBFS. Far from horrible, but not ideal either.
If you're going from 24-bit sources to 16-bit CDs, then yeah you have 20-40dB to play with depending on your converters.