Due to global megatrends, production lines are getting faster. Because of the parallel kinematic architecture, the delta robot has a very high mechanical advantage in performance and flexibility when compared to traditional articulated robots, and even cartesian robots.
Delta robots are purpose-built for pick-and-place, going back all the way to their inception.
Typically, you’d need a Delta robot if you have a rate that’s going to be sustained—a lot of parts flowing down the conveyor belt, hundreds of parts per minute. There are other robots that can do fast rates, but they can’t keep up with the rate of a delta without overheating or working over their motor duty.