Covering your landings, remaining threatening when recovering/getting off the ledge, punishing a reckless approach.
Any situation in which you could land somewhere, the KO Punch becomes threatening before you land. It also becomes a bit more flexible with B-Reversing and fastfalling aerials.
It's useful, but not really world-changing. Pretty nice anti-platform camping tech, but it still requires Mac to be in the air to begin with. Start-up is significant since it relies on the use of an aerial ahead of time, but as a result, this has good basic mix-up potential with a regular fastfall landing -> KO Punch.