Shoot tipping is part of canopy management that involves removing the top of the growth tip of a shoot. This temporarily changes the flow direction of nutrients and water and therefore encourages lateral shoot growth, which in turn will provide additional leaf surface which increases photosynthesis during fruit ripening.
This practice would normally be done after fruit set but Peter Hayes has advised us that that vine tipping may also divert carbohydrate to flowers and help the fruit set process. It won't overcome poor flower development or reinstate aborted flowers but where vigor is high may help. With the recent poor weather we need all the help we can get!