The benefit I find from milling the deck is that when a ship is destroyed, all the damage cards go into the discard pile face up. That would allow you to figure out what crits are out of the way and what may be more likely to come. Perhaps effecting a decision later on to spend a focus/evade to avoid a possibility. How often will that come into play? Hasn't yet for me while i've been playing, but you never know i suppose.