Worst case outcome is a fumble. Then is a clock stoppage which would be an offensive penalty that gets declined, going out of bounds or like we saw an injury where the player can’t get off the field on his own.
So that is the risk of running the ball vs taking a knee to ensure the clock keeps running.
Unless you are legitimately trying your best to get the first down best to take the knee on third down. Heck even all 3 downs. Again, never know if an OL will hold or get their hands into the face of a DL. Remember back when Atl had first and 10 inside the NE 25 up 8 in the final few minutes. Got 2 penalties which pushed them outside FG range to make it a 2 score game at that point. So that can happen when you run the ball.