Loose hamstrings and buttocks allow you to transfer your weight correctly on the backswing and downswing for maximum power
If you are practicing and start hitting bad shots then step away from the ball and work on re-establishing solid contact with a few bump shots in order to get the feel for center clubface hits
Help kids fix their slice by standing in front of them while they take practice swings and have them release their downswing straight down the line toward you