The ghost serve is not really a popular term. I think it became known when a video of Ma Lin serving was shown with the title ghost serve.
In a match situation players don't try the serve that bounces back over the net. The reason is that to do this with any consistency the serve needs to be really slow so the spin can have enough effect to bring the ball back over the net and also the serve tends to be quite high. It would allow to much time for the receiver to move down the side of the table and hit it for an easy winner.
Players get a lot of advantage with their regular serves and this is what they tend to focus on. Players certainly use heavy backspin serves (and mix these up with no spin serves to deceive their opponents) but these are usually low and fast and short so that the ball would bounce at least twice on the table making it hard to attack.
So it is certainly worth learning how to impart lots of spin on your serves but spend more time working on keeping the ball really low over the net and working on subtle variations of your serve which will confuse your opponent.
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