A ball shall be cleaned and marked only once when on the putting green.
Some players take up to 60 seconds to mark, replace the ball, align the ball, remove the marker.
This would save 30-40 minutes on the time of a 4 Ball.
Time is the reason the game is becoming less popular.
No penalty for striking another players ball. The opponent can ask for the player to mark the ball if it is directly on his line and the player may then opt to either putt or mark.