It's a common trope in the visual design of dragons, giant bats and other fictional flying beings to have wings that appear to be severely torn, cut, pierced, and otherwise worn down. It's also quite likely that the wing of a flying creature would be a prime target for its enemies in combat, so it might take on that appearance unwillingly.
My concern is that this would obviously affect the flying beast's ability to fly, but I'm not keen on the specifics of that. I can make a wild guess that this: would be solid enough to support flight, and that this: would let entirely too much air though to have sufficient lift remaining.
What I want to know is, at what point do holes in the wing become too much of a hindrance for the animal to achieve and sustain flight?
My interest is especially focused on combat with dragons. Would a single lucky sword-stroke, bite, or bullet be enough to ground the beast or would it take dozens of hits until half the surface area of the membrane is gone?