The serving team's first shot after serve and return: soft and high into the opponents' kitchen instead of hard — it buys you the time to move up to the net.
The third ball is the tactical switch for the whole point. After the serve and the return you are stuck at the back while your opponents own the net — a hard drive changes nothing about that, it only invites a counter. The soft drop, by contrast, takes the pace off, forces your opponents to play the ball upward, and hands you the seconds you need to move up to the kitchen line with your partner. The typical fault is impatience: swinging hard because early on the drop often floats too high or finds the net. It takes time to bed in — and still no other shot repays practice as well, because none improves your position as much. And when it fails, the reset at the net is your lifeline: absorb the hard ball softly and let it fall back into the kitchen instead of swinging back.