Is height an advantage or disadvantage for table tennis players?

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Not much...True taller players have longer reach, but may be a bit slower due to their body vs heart propotion, and shorter people have a bit shorter reach but are often faster because of the heart has less distance for blood to be pumped to the body and pumps easier and faster.

Having a longer reach is an advantage. Taller people typically have longer arms, so, all other things being equal, I would say yes.

All other things are never really equal. Speed, quick reflexes, coordination and intuition about how the ball moves are all, almost certainly, bigger advantages than longer reach or higher eyes.

Having higher eyes might help in some situations: better visibility and perspective on some shots, but perhaps worse perspective on others.

If you are too much above the table however I believe it reduces the accuracy of your hits, especially for low balls. Thus a tall person might have be forced to bend down and slouch while playing leading to discomfort and greater fatigue. But for high balls then it may be easier for a tall person to smash more accurately, unfortunatley there are usually not as many high balls as low balls. Giving tall people a significant disadvantage over shorter or normal sized people.