High,
It's a combination of all the above. I'm an experienced diver (sky) lmao. It's not so much "hitting the plane". When you exit you are immediately hit by a 140 MPH wind that leaves really no chance of you being diverted into the aircraft.
It is to protect you from other divers who may inadvertently hit you which at those speeds is like a bullet. The guidlines that hold the chute in place are high tensile nylon but have been known to snap on opening. There are 14 of them so if you lose one it's no biggie but if that "one" slices your ear off or smacks you unconscious it just became a "biggie".
Lastly to protect from ground/landing accidents. If you coming down with no chute at all, a helmet is the last of your worries. But encounters under a chute with an experienced pilot have been know to see trees, buildings and cars even with the most experienced jumpers. The weather can be a BITCH!
