The first battle in Yemen ended at the cost of Joseph's minor wound. The price wasn't high, but Gao Yang was still somewhat dissatisfied.
A minor wound is still a wound, it still needs time to recover, and the only real difference between a minor wound and a serious one is just a bit of luck. If the bullet or shrapnel had deviated just a little, that minor wound could have become a serious one, or even fatal.
If someone gets hurt in every fight, even if it's just a minor wound, Satan can't afford it.
What Gao Yang worried about wasn't that too many wounded would affect combat strength and thereby disrupt their plan in Yemen; he just didn't want anyone in Satan getting hurt, let alone killed.
Since the difference between a minor wound and a serious one is often just a tiny bit of distance, basically just a bit of luck, then luck obviously becomes an extremely important thing.
