The setter dump is about more than just an opportunity to score points. Even when it's unsuccessful, it gives the defense one more thing to think about, which often opens up better attacking opportunities for the hitters.
"Even when setters are in the back row, you always want them to be offensive," says Jed Stotsenberg, coach at Wave Volleyball in Del Mar, California. "(Sometimes) I give my team a dump quota and say, 'You're going to have to dump the ball 10 times in this match.' Even if we're not successful, it's going to keep the block on their heels and it's going to open up stuff for the other players."
As former Stanford coach John Dunning explains in this video on disguising the dump, successful setter attacks often depend on the setter holding his/her hands in a setting shape long enough so the defense can't get an early read on the tip.
For a quick look at how to defend the dump, check out this video on reading the setter from USA Youth National Team Coach Jim Stone.