I learned way too late in life that I was mixing to quietly. You really need to move some air to hear what the bottom end sounds like, and some speakers just sound better and flatter louder. When you're too quiet your mixes tend to turn out wimpy. That said, the way it usually works for me is to listen loudly (90+dB SPL) for the first half of the mix, then when the real intricate balances are happening, back it off to just above a whisper. I can really hear balances well at that level.
That's what works for me; it may be different for you. We each have to find what works for us, then stick to it.