The Funk

What you are looking for is signal to noise ratio. As long as you have a clear signal you can actually record quite low in the digital realm. The best signal to have is what I would call a "healthy signal". robust enough that its really there and doesn't have to be boosted (adding noise) but not so hot that it takes over anything. Remember, amplitude sums. When you have 2 tracks peaking at -6, then your master is peaking at -3. (I think). The more tracks you have the higher the master goes. So in order to mix, you will be pulling everything down anyway. Which means you add more math to the situation and get less usuable range out of your faders. thus don't record too hot.