[member="Micah Talith"], [member="Fiolette Yvarro"]
After reading over the sub, it's pretty evident that the shuttle cuts a hole in the hull of whatever it is breaching, which depressurizes it. Once the pilot of the shuttle decides to do so, the shuttle then presses down closer to the hull and seals it with the belly of the shuttle before deploying it's troops. The tactical benefit if that you suck the defenders into space, giving yourself a nice little beachhead. The drawback is that you suck the defenders towards you... So if they are already in vacuum-capable armor and equipped with, say, grappling lines... You now have a squad or platoon of angry Marines/troopers trying to destroy your shuttle with blasters, grenades, and plasma torches.
Also, it would be entirely optional to the person controlling the shuttle to decide how quickly to seal off the hole, to control how much atmosphere (and personnel) gets sucked out.