In the old days, you had to load [gun]powder into your weapon along with the projectile. Dry powder burns hotter and faster, shooting your projectile farther, faster, straighter, and deadlier.
Also in the old days of naval warfare, if you won a battle it was accepted that the other ship (what was left of it) was your prize. Everyone in the chain of command had a predefined percentage of the ownership, with an eighth or so divided evenly among the common sailor. This ownership stake was converted into cash either by your own government or a private prize broker depending on the circumstances.
An exceptionally successful deployment would leave the common sailor with enough money to retire; the captain of the ship might even become fabulously wealthy.
But anyway. Keeping your powder dry on the way to the battle is important if you want to win, get your prize, and retire from all that cash.
I think a lot of VC and IB take the metaphor way too seriously, but you can see how many parallels there are!