It doesn't create tension. It just creates "throwaway" games.
Its basically "I kept a two-land hand, because the Mulligan system is very punishing for no guaranteed improvement on your hand. If I draw a 3rd land before my third turn, I'm set. Oh, I didn't. Guess I lose."
Or "Alright, I've drawn 4 lands in a row. Certainly, I can't keep drawing lands. Oh, I did. For the next 4 turns. Guess I lose."
It sucks when it happens to you, and even when it happens to your opponent, it's not a win you're particularly happy about. Because you didn't win because of anything you did, but rather because of the game's RNG.