Wide, Stable Base.
We need a wide stable base whenever we apply force laterally. We should never have our body weight supported by a hand tool. Two examples of injuries are (1) A worker falling forward when the impact gun he was leaning on dropped after loosening a nut; and (2) A worker falling backward when a wrench broke free from a nut. If you cannot keep your weight within your stance, figure out a safer approach to the task.