I would expect a military goal is to take as many enemy combatants out of the fight as possible, not necessarily kill them. I guess it depends on how close they are to you and what immediate threat they produce. Using a super-hightech "One Shot Stopper (tm)" bullet would take out ... one enemy combatant. However, ball ammo would wound one, and then busy up a few others caring for and hauling their comrade around. So you've taken more enemy combatants out of the immediate fight. The longer it takes your ball ammo wounded target to finally die, the more enemy resources you tie up.

In close quarters urban combat the above theory wouldn't hold water. You'd want to take them out quickly so they don't shoot you back while they're hanging on waiting around to die.