Karch Kiraly talks in this video about how to target weak passers and specific areas of the court with a float serve.
One strategy is simply to locate a player who is a less-than-great passer and go after her with a hard, flat float serve.
Another strategy is serving to Zone 2, which means the passer has to take the ball near the setter. This can disrupt the connection between the passer and setter and tangle up the opposing team’s offense.
A third tactic is to serve different depths. “If I’m a passer,” Kiraly says, “I can identify (a serve moving) left and right a lot quicker than I can identify depth.”