Running the cards twice is a common practice among the top professionals in high stakes ring games. Daniel Negreanu mentions this form of finishing an "all in" hand many times in his forum. The deal is that when there are two players all in with a coinflip situation, one player might propose to run the board twice. I have done this a few times at my home game. I had JJ vs AK all in preflop. I offered him to run it twice even though I am the slight favorite. My goal in cash games is to break even. Yes it is nice to have a big win, but a 50/50 is not the kind of odds
I want to acheive a big win. He agreed and we dealt the board twice. He spiked an ace on the flop the first deal but my jacks held up the second time around. Therefore we split the pot and both happily went on to have a winning session. I believe that this is a smart tactic to use when a lot of money is on the line in a coinflip situation and I believe that it will be seen in cash games more often in the future.