Second Serves
Most players hit their second serve with more spin than their first serve. Hitting it with spin allows them to hit it higher over the net with the spin bringing it down before it goes long. Sidespin (slice) forces the receiver to watch it more closely to see how much it curves thereby discouraging them from drilling it. Topspin serves bounce higher (kick). Most professional players hit the second serve with topspin. The difference in timing from the first serve often causes a weak return. Most players must learn to take it early in order to return it at all.