I knew that if you didn’t have your rifle perfectly level, it would affect where the bullet would actually impact. That said, I didn’t know much else about it.
This recently released video from the National Shooting Sports Foundation featuring Todd Hodnett of Accuracy 1st does a good job of explaining both the impact of cant and how to account for it when aiming.
As to shooting with the rifle 90 degrees off of center, I had never seen that before. I believe he is correct that it does have tactical applications.